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Öğe Analysis of amplitude and slope diffraction coefficients(2013) Tabakcioglu M.B.; Cansiz A.The diffraction mechanism is used for field prediction in both light and shadowed regions. Slope and amplitude diffraction coefficients are vital to predict the field strength at the receiver accurately. In this paper, amplitude and slope diffraction coefficients for one of the ray theoretical models, the slope uniform theory of diffraction with convex hull (S-UTD-CH) model, are analyzed. Moreover, diffraction coefficients are given for knife-edge and wedge structures. © TÜBİTAK.Öğe Application of S-UTD-CH model into multiple diffraction scenarios(2013) Tabakcioglu M.B.; Cansiz A.Propagation prediction models based on ray tracing in coverage estimation for digital broadcasting systems are compared. Geometrical Theory of Diffraction (GTD), Slope Uniform Theory of Diffraction (S-UTD), and Slope UTD with Convex Hull (S-UTD-CH) models are compared for computation time and propagation path loss. S-UTD-CH model is optimum model with respect to computation time and relative path loss. © 2013 Mehmet Baris Tabakcioglu and Ahmet Cansiz.Öğe Clarification of magnetic levitation force and stability property of multi-seeded YBCO in point of supercurrent coupling effect(Elsevier Ltd, 2016) 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 Jc(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 Bzpeaks than the other arrangements with one Bzpeak 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 Bzpeak 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. © 2016 Elsevier B.V.Öğe Comparison and analyzing of propagation models with respect to material, environmental and wave properties(Applied Computational Electromagnetics Society (ACES), 2014) 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. © 2014 ACESÖğe Levitation and guidance force efficiencies of bulk YBCO for different permanent magnetic guideways(Elsevier Ltd, 2015) 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. © 2015 Elsevier B.V. All rights reserved.Öğe S-UTD-CH model in multiple diffraction geometry(2010) Tabakcio?lu M.B.; Cansiz A.Calculation of relative path loss of electromagnetic wave in multiple diffraction geometries is important. In this respect, many diffraction models have been introduced. There is a trade-off between computation time and accuracy of estimated field strength. Some models have higher computation time with lower accuracy, or vice versa. In this study, Slope UTD with Convex Hull (S-UTD-CH), optimum model for accuracy and computation time, is introduced briefly, and simulation results are given. S-UTD-CH model is based on slope diffraction (S-UTD) including slope terms of UTD, and convex hull (CH) method. It is observed in simulation how polarization types, interior wedge angle, conductivity and relative permittivity of wedge affects the relative path loss. Moreover, comparative results of different models with respect to accuracy and computational time for a given profile are presented in this study.
