Study of AC Loss Characteristics of HTS-coated Conductor with?Magnetic Substrate Using FEM Analysis

A high-T _c superconducting (HTS)-coated conductor with a magnetic substrate is promising as a low-cost conductor because Ni alloy can be well texturized by a simple process. However, it has been reported that the magnetism of the substrate makes an AC transport current loss and an AC magnetization loss increase from those losses of the HTS-coated conductor of a nonmagnetic substrate sharply. However, the assembled conductor which bundled many HTS-coated conductors with a magnetic substrate is hardly reported. In this paper, the AC loss and the current distribution in the superconducting layer of the HTS-coated conductor with a magnetic substrate are analyzed using the edge-based hexahedral finite element method (FEM) taking account of both the nonlinear E?CJ characteristics and the nonlinear magnetic property of the substrate at 77 K. Moreover, AC loss characteristics of HTS-coated conductors with a magnetic substrate arranged with an infinite number of the coated conductors are examined and the effect of the gap length between adjacent conductors on the AC loss is also investigated.     

Losses in Coated Conductors Under Nonsinusoidal Currents and?Magnetic Fields

The study of AC losses in superconducting wires and tapes is usually restricted by consideration of applied sinusoidal currents and/or magnetic fields. However, currents in electric power systems contain a wide variety of harmonics. The currents become strongly nonsinusoidal in the operation of converters and nonlinear reactors, and during transient and overload conditions. Recently it has been shown that the contribution of higher harmonics to AC losses in superconducting bulk and thin film samples can be tens times larger than in normal-metal samples of the same form, and the 5% harmonic can increase the losses by up to 20%. Here we report the results of an analysis of the influence of higher harmonics of the current and magnetic field on AC losses in coated conductors. Analytical expressions are obtained in the framework of the critical state model, neglecting the response of the normal-metal substrate and stabilization layers. Losses in the superconducting and normal-metal parts of a coated conductor are compared for various designs of the conductor. It is also shown that the 5% third current harmonic can increase the losses in the normal-metal parts by up to 60%. This increase is caused by a nonlinear response of the superconducting layers and should be taken into account in the determination of the optimal operation regimes of superconducting devices.     

3D-Modeling Numerical Solutions of Electromagnetic Behavior of HTSC Bulk above Permanent Magnetic Guideway

This paper presents a 3D-modeling numerical method using finite element method (FEM) to simulate the electromagnetic behavior of high-temperature superconductors (HTSC). The models are formulated by the magnetic field vector method (H-method). The resolving code was written by FROTRAN language. The electromagnetic properties of HTSC are described though Kim critical-state model. The magnetic fields and current distribution in the bulk HTSC in the applied non-uniform external magnetic fields generated by the permanent magnetic guideway (PMG) are obtained using the proposed method. The magnetic levitation forces by the interaction between the bulk HTSC and the PMG are calculated. In order to validate the method, measurement of the vertical force between a bulk YBaCuO(YBCO) and a PMG is obtained. The measurement and simulation results show good matching. This method could be used in the HTSC magnetic levitation transportation system optimization design.      

Progress in Numerical Simulation of Solidification Process of Shaped Casting

Solidification simulation of manufacturing shaped casting which plays an important role in asSuring the soundness and quality of castings, in minimizing the trial production time and in reducing the manufacturing cost becomes one of the hottest topics of the new research frontiers of foundry technology at home and abroad. Practical three dimensional computer numerical simulation system for temperature distribution during solidification as well as shrinkage cavity and porosity prediction has already been put into application all over the world. Further fundamental researche5 on fluid flow, thermal stress and micro-modeling as well as practical approaches of numerical simulation of solidification process of shaped castings for routine analysis of foundry industry are still underway.     

A Simulation on Levitation Force and Guidance Force of the HTSC Bulk Under the Permanent Magnetic Guideway’s Stochastic Excitation

Journal of Superconductivity and Novel Magnetism - In the actual operation of the high temperature superconducting (HTSC) maglev, due to the irregularity of the permanent magnetic guideway (PMG),...     

Numerical Simulation of Morphology and Microsegregation Evolution during Solidification of Al-Si Alloy

A stochastic model coupled with transient calculations for the distributions of temperature, solute and velocity during the solidification of binary alloy is presented. The model can directly describe the evolution of both morphology and segregation during dendritic crystal growth. The model takes into account the curvature and growth anisotropy of dendritic crystals. Finite difference method is used to explicitly track the sharp solid liquid (S/L) interface on a fixed Cartesian grid. Two-dimensional mesoscopic calculations are performed to simulate the evolution of columnar and equiaxed dendritic morphologies of an AI-7 wt pct Si alloy. The effects of heat transfer coefficient on the evolution of both the dendrite morphology and segregation patterns during the solidification of binary alloys are analyzed. This model is applied to the solidification of small casting. Columnar-to-equiaxed transition is analyzed in detail. The effects of heat transfer coefficient on final casting structures are also studi     

Doping Dependence of Magnetic Field Penetration Depth in Kinetic Energy Driven Cuprate Superconductors

The doping and temperature dependence of the magnetic field penetration depth in cuprate superconductors is studied based on the kinetic energy driven superconducting mechanism. It is shown that the magnetic field penetration depth shows a crossover from the linear temperature dependence at low temperatures to a nonlinear one in the extremely low temperatures.     

Transport AC Loss Measurements and Simulations in Bi-2223/Ag Tape with?Ni Cover at?the?Edges

Measurements on Bi-2223 multifilamentary tapes covered on edges by nickel showed a substantial AC loss reduction (Gömöry et al. in Supercond. Sci. Technol. 22: 034017, 2009) and increasing critical current of the tape. Here we present a systematic study of this effect involving numerical simulations. The samples were prepared by deposition of Ni layer on commercial Bi-2223 tape. After measuring the critical current and the transport AC loss, cross-section photos are taken and the properties of nickel cover determined to be used in the calculations. We observed that with increasing Ni thickness the transport AC loss of the wire is decreasing in the high current region. In low current region because of the magnetic hysteresis in the Ni cover the transport AC loss of the Ni covered tapes are larger. Our calculations according to the method which is detailed in Gömöry et al. (Supercond. Sci. Technol. 22:034017, 2009) show good agreement with measurements.     

Numerical Calculation of Trapped Magnetic Field for Single and Multiple Bulk Superconductors

In this work, the trapped magnetic field was calculated using the sand-pile model and Biot–Savart law. The numerical simulation of the trapped magnetic field was performed varying the sample shape and dimensions, distance between the sample surface and observation point. In addition, the magnetic field characteristics of superconducting bulk arrangement in an array was determined. The trapped magnetic field was found to be depending on the sample shape and dimensions and distance between the sample and observation point. It is observed that, when the distance from the surface is larger, the value of the trapped magnetic field decreases, but the variation of the trapped magnetic field becomes small due to averaging the distribution of the trapped magnetic field.     

Study on Numerical Simulation of Mold Filling and Solidification Processes under Pressure Conditions

The mold filling and solidification simulation for the high pressure die casting (HPDC) and low pressure die casting (LPDC) processes were studied.A mathematical model considering the turbulent flow and heat transfer phenomenon during the HPDC process has been established and paralled computation technique was used for the mold filling simulation of the process.The laminar flow characteristics of the LPDC process were studied and a simplified model for the mold filling process of wheel castings has been developed.For the solidification simulation under pressure conditions,the cyclic characteristics and the complicated boundary conditions were considered and techniques to improve the computational efficiency are discussed.A new criterion for predicting shrinkage porosity of Al alloy under low pressure condition has been developed in the solidification simulation process.     

Numerical Study and Optimization of Hydrothermal Characteristics of Mn–Zn Ferrite Nanofluid Within Annulus in the Presence of Magnetic Field

Flow and heat transfer characteristics of water–MnZnFe₂O₄ magnetic nanofluid through an annulus were evaluated under the effect of non-uniform magnetic field using the two-phase Euler–Lagrange method. The effects of concentration, size of particles and magnitude of magnetic field gradient were investigated. The concentration distribution was found to be non-uniform, with its value lower near the walls. Velocity profile becomes flatter at the cross section of the annulus by applying the magnetic field. Increasing particle size, concentration and magnitude of the magnetic field gradient enhance the convective heat transfer coefficient. The effect of increasing magnitude of the magnetic field gradient on heat transfer and pressure drop is more significant for larger particles. Models of convective heat transfer coefficient and pressure drop were obtained in terms of the effective parameters using neural network. Meanwhile, optimization was implemented via genetic algorithm coupled with compromise programming technique in order to achieve the conditions with maximum heat transfer and minimum pressure drop. Based on the results obtained from optimization, application of the magnetic field is only recommended when heat transfer is considered to be more important than pressure drop.     

Finite Element Simulation of Temperature and Current Distribution in a Superconductor,and a Cell Model for Flux Flow Resistivity—Interim Results

A critical problem arises when current distribution in a high-temperature superconductor and its stability against quench shall be predicted: is it correct to assume homogeneous temperature distribution in superconductors, in general or only in LHe-cooled devices? The finite element analysis presented in this paper shows that during the very first instants following a disturbance, like single Dirac or periodic heat pulses, or large fault currents, temperature distribution in a BSCCO 2223 conductor is highly inhomogeneous. This is because disturbances, of transient or continuous, isolated or extended types in conductor volumes, create hot spots of comparatively long life cycle. As a consequence, separation between Ohmic and flux flow current limiter types, or decisions on the mechanism that initialises current sharing, cannot be made definitely. A semi-empirical cell model is presented in this paper to estimate flux flow resistivity in multi-filamentary superconductors in a successive approximation approach. Weak links are modelled, as nano- and microscopic surface irregularities and corresponding resistances, in analogy to thermal transport. Though the model requests input of a large amount of data (dimensions, porosities, field-dependent quantities) that still have to be verified experimentally, it is by its flexibility superior to ideas relying on, for example, imagination of separate, non-interacting chains of strong and weak links switched in parallel. In particular, and in contrast to the standard expression to calculate flux flow resistivity, the cell model suggests to replace solid conduction by an effective resistivity, a method that is more appropriate for multi-filamentary conductors. The paper also discusses integration time steps in numerical simulations that have to be selected in conformity with several characteristic times of current and thermal transport.     

Visibility of the Aharonov–Bohm Effect in a Ring Coupled to a Fluctuating Magnetic Flux

We consider the visibility of the Aharonov–Bohm effect for cotunneling transport through a clean one-channel ring coupled to a fluctuating magnetic flux. We concentrate on the modification of the destructive interference at ₀ /2 by the fluctuating flux, since changes in the magnitude of the current away from this point can also be caused by renormalization effects and do not necessarily indicate dephasing. For fluctuations arising from the Nyquist noise in an external coil at T=0, the suppression of the destructive interference shows up only in a contribution proportional to V ³ , and therefore does not affect the linear conductance. In this sense, the Nyquist bath does not lead to dephasing in the linear transport regime at zero temperature in our model.     

Penetration of the Material of Particles from a High‐Velocity Flux in Collision with a Steel Obstacle to Large Depths

Experimental data on the punching of steel obstacles of thickness 20 mm are given, which show that, in collision and penetration, the particle and obstacle materials go out onto the rear side of the obstacle in the form of thin jets and their interaction with the package of electronic elements is responsible for the degradation of these elements located behind the obstacle.     

Measurement and Separation of Magnetic Losses at Room and?Cryogenic Temperature for Three Types of Steels Used in?HTS?Transformers

The magnetic losses of steels used in high temperature superconducting (HTS) transformers are very important for the transformer??s efficient design and for a correct choice of operating conditions. This introduced the necessity to analyze electrical steels behaviour at low temperature in order to characterize their magnetic properties and, in particular, the magnetic losses. Three steels were chosen for this analysis: one non-oriented silicon steel and two different grain-oriented silicon steels. Several measurements of total magnetic losses were made at 77 K and 298 K and for different values of maximum magnetic induction, B _max?, in order to compare the dependence between them at both temperatures. These results are presented in Pronto et al. (European Conference on Applied Superconductivity, 2009). Subsequently, measurements of hysteresis losses (DC regime) at both temperatures were also made in order to obtain all terms of magnetic losses (hysteresis, classical eddy-current losses, and excess losses). The results are presented in this paper.     

AC Loss of a Multi-Layer per Phase Tri-Axial HTS Cable with?Balanced Current Distribution

Recently, high-temperature superconductor (HTS) cables have been widely studied because of their compactness and high power capacity compared to conventional copper cables. In HTS cables, AC loss is an important issue since large losses reduce the efficiency of the power line. Among HTS cables, tri-axial cable is under intensive investigation recently, since it has a smaller amount of HTS tapes, small leakage fields and small heat loss in leak when compared with the three single-phase cables. For realizing high current capacity, more than one layer is required for each phase; therefore AC loss of the multi-layer tri-axial HTS cable should be carefully examined. In the tri-axial cable, different phase currents produce the out-of-phase magnetic fields on the other phase layers. In case of multi-layer arrangement, net magnetic fields on layer surfaces may exceed the penetration field of the HTS tape. Therefore in this paper, we analyze the AC loss of a tri-axial HTS cable which is composed of two layers per phase. Here, we treat the tri-axial cable which consists of two different longitudinal segments and thus satisfies balanced phase and homogeneous current distribution condition by controlling twist pitch and length of separate segments.     

Enhancement of a Magnetic Field in a Perfectly Conducting Medium on Penetration of a High‐Velocity Jet into It

We consider the possibility of enhancement of a magnetic field created in a conducting medium on penetration into it of a highvelocity striker moving across the magneticinduction lines. For the case of a perfectly conducting target, an estimate is obtained for the rate of increase of the field intensity in the region of contact with the head part of the striker. A dimensionless parameter is introduced that characterizes the relationship between the rates of generation and diffusion of the field on penetration into a material of finite conductivity. Based on a model that takes into account the force action of a compressed field, the special features of the flow that arises on penetration of a highvelocity cumulative jet into a perfectly conducting target with a transverse magnetic field are analyzed.     

Atomistic Simulation of Phase Transformation and Fracture in Ordered Intermetallics

A review of computer simulations carried out at our Center for Materials Simulation applied to stud-ying the different atomistic processes of fracture and displacive (martensitic) transformations is pres-ented.Since these processes can happen extremely rapidly and involve only a small number of atomsinitially,they are ideally suited for molecular dynamics type simulations which can currently onlyspan times of the order of one nanosecond and involve at most a million atoms.A method is alsopresented for simulating much larger samples for much longer times through the use of theMonte-Carlo technique combined with a Ginzburg-Landau free energy functional,where the rele-vant material parameters are determined from molecular dynamics runs on the same alloy system.Asummary of studies on fracture simulations in the ordered intermetallics NiAI and RuAl is given,aswell as a discussion of the observation and analysis of the heterogeneous nucleation of themartensitic transformation in NiAI which shows localized soft mode phenomena.It is concluded thatcomputer simulations,whether of the atomistic molecular dynamics type or of the larger scaleMonte-Carlo variety,are rapidly becoming of greater and greater use in understanding the propertiesof solids under a wide rancle of temperature and stress conditions.     

Corrosion Penetration and Crystal Structure of AA5022 in HCl Solution and Rare Earth Elements

Al-alloy (AA5022) corrosion penetration (CP) and crystal structure were investigated after running static immersion corrosion tests in 1 mol/L HCl solution and different concentrations of rare earth elements (La3+), (Ce3+) and their combination, at different temperatures. X-ray diffraction (XRD) was used to examine the surface structure before and after immersion, and secondary electron detector (SED) was operated to study surface morphology. In 1 mol/L HCI solution the corrosion penetration increased with increasing temperature and immersion time. The increase of La3+ concentrations up to 1000×10-6 g/L led to the decrease in the corrosion penetration, and the decrease in Ce3+ concentrations up to 50×10-6 g/L decreases the corrosion penetration of the alloy. Mix3 (combination of La3+ and Ce3+) dramatically reduced the corrosion penetration. This suggests that a synergistic effect exists between La3+ and Ce3+. The reaction kinetics both in absence and presence of La3+ and Ce3+ and their combination woul