Ozturk, K.; Guner, S.B.; Abdioglu, M.; Demirci, M.; Celik, S.; Cansiz, A.

The higher magnetic levitation force and related stiffness values are very important for Maglev and magnetic bearing applications. Also, larger superconducting surface area is needed for continuous and larger magnetic mediums with different geometries and dimensions in real scale industrial applications of superconducting systems. In this study, the cylindrical YBCO superconductors were fabricated by top−seeded melt growth (TSMG) method in single and two−seeded forms with different seed distances and then the magnetic force and stiffness measurements were carried out by three axes magnetic force measurement system in different cooling heights (CH) of 20 mm and 75 mm. Additionally, a new analytical method, based on the magnetic dipole approximation, is proposed to calculate the levitation force in this study, named as Modified Advanced Frozen Image Method (MAFI), since although the Advanced Frozen Image Method in literature can calculate the levitation force with hysteresis, this method does not include the size effect of the superconductor. In the experimental studies, it is seen that the maximum levitation force values obtained by PMG with three PMs (named PMG−1) are more than two times higher than that of obtained with single PM for all samples with different distance of seeds, because of the higher magnetic flux distribution of related PMG arrangement than the single PM. In addition, the maximum magnetic levitation force value firstly increased and then decreased due to current coupling effect weakness by increasing distance of seeds. The calculated analytical levitation force results are not compatible with the experimental results without current coupling effect, but a well agreement is observed when the current coupling effect is taken into account in calculations. Also the MAFI method was tested with different dimensions of superconductors and the obtained results indicated the success of the proposed method. The maximum levitation force values obtained with MAFI method increased with increasing dimensions of HTS and PMs. Thus, one can say that the MAFI method is useful for the levitation force calculations between multi−seeded superconductors and PMGs with different dimensions and for different CHs. As a result, the analytical levitation force values obtained with the MAFI method are agree with the experimental levitation force sufficiently and this method can give fast calculation results without any divergence problem. This method can be thought as an alternative to the numerical calculation methods, having serious divergence problems for much amount and bigger size superconducting samples, therefore it will be useful to clarify bulk superconducting properties as supporter to the experimental studies.

AtıfScopus19·WoS18·OpenAlex22

İncele

Ozturk, K.; Kabaer, M.; Abdioglu, M.; Patel, A.; Cansiz, A.

In our study as different from the literature, which are mostly related to superconductor fabrication, application and optimization, especially physical origins of bulk supercurrent generation, magnetic levitation and stability properties of the multi-seeded YBCO superconductor are investigated in point of supercurrent coupling effect. Besides the experimental measurements, a simplified simulation of the supercurrent coupling in the multi-seeded bulk YBCO is carried out based on the experimental J(c)(B) data taken from literature and using the critical state method and H-formulation together in COMSOL Multiphysics package, to further elucidate the mechanism of supercurrent generation and guidance force. The bigger guidance force and lateral magnetic stiffness values of PMG-B arrangement with three B-z peaks than the other arrangements with one Bz peak in small cooling height of 5 mm are attributed to the more robust individual intragrain supercurrents, rather than intergrain supercurrent, due to the position coincidence in the z-direction between grains and permanent magnet poles. Additionally, it can be said that PMG-C arrangement with one Bz peak getting to the maximum guidance force value when the cooling height increase from 5 mm to 15 mm, points out for large cooling height the intergrain supercurrents dominate, whereas for the small cooling height the intragrain supercurrents have most effect on the guidance force. Also, performed the supercurrent simulations, using different current flow constraint ratio f (or supercurrent coupling parameter), clearly reproduced the qualitative change in the trapped field profile when the allowed intergrain current compared to no intergrain current (f = 0). It is thought that the presented results, related to the supercurrent generation, coupling mechanism and their effect on levitation and lateral force properties, have utilization potential for researches not only they study on new multiseed superconductor fabrication method, but also they study on superconductor applications. (C) 2016 Elsevier B. V. All rights reserved.

AtıfScopus29·WoS30·OpenAlex30

İncele

Abdioglu, M.; Ozturk, K.; Gedikli, H.; Ekici, M.; Cansiz, A.

The development of superconductor Maglev systems depends on various disciplinary studies due to the inherent composition of available technologies. Because the fabrication cost is very effective on the Maglev, the requirement of the efficiency improvement focuses the researchers on the design considerations. In this study, the guidance force, the magnetic levitation force (MLF) and magnetic stiffness of different permanent magnetic guideway (PMG) arrangements were investigated in different cooling heights (CH) to enhance the efficiency of Maglev system. The single domain cylindrical bulk YBCO superconductors fabricated by top seeding method with the diameter of 45 mm and the height of 15 mm were used as HTS. Magnetic field distributions of the PMGs were calculated by finite element method to determine optimum HTS-PMG arrangements. We have used auxiliary onboard permanent magnets with YBCOs to improve the MLF of three pole Halbach PMG arrangements. It is seen that the efficiency of Maglev systems can be improved by using suitable HTS-PMG arrangements. In this study cost efficiency of the integrated levitation and guidance force ((Fz)max(Fx)max/(SPMG ∗ Cost)) was also determined. It is inferred from this study that the cooling height and PMG-HTS arrangement are key parameters for guidance force, levitation force, magnetic stiffness and efficiency of Maglev systems. It is believed that this study will supply useful references for practical application of HTS Maglev systems.

AtıfScopus60·WoS59·OpenAlex61

İncele

Tabakcioglu, M.B.; Ayberkin, D.; Cansiz, A.

This paper presents a study on a class of algorithms based on Uniform Theory of Diffraction (UTD) for multiple diffractions. Within this context Slope UTD with Convex Hull (S-UTD-CH) model based on Slope UTD and Fresnel zone concept was reviewed. S-UTD-CH model can be used for fast and more accurate field prediction for multiple diffractions in transition zone. An extensive simulation results for comparison of UTD based algorithms with respect to the computation time and accuracy was provided. Furthermore, the study shows how relative permittivity constant, conductivity and inner angle of wedge and polarization type affect the relative path loss.

AtıfScopus6

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