Sharif Digital Repository

This paper presents analysis of electric field distribution and optimization of C-type corona rings for 400 kV V-insulator strings composed of ceramic insulator units which are the most common configuration of overhead transmission lines. These strings are equipped with corona rings to enhance the insulation performance regarding to the effect of these rings on the insulation function and potential and electric field distribution. 3D field simulations are performed for the C-type of corona rings with different dimensions by software based on FEM analysis  

We show a methodology for how to construct Dirac points that occur at the corners of Brillouin zone as the Photonic counterparts of graphene. We use a triangular lattice with circular holes on a silicon substrate to create a Coupled Photonic Crystal Resonator Array (CPCRA) which its cavity resonators play the role of carbon atoms in graphene. At first we draw the band structure of our CPCRA using the tight-binding method. For this purpose we first designed a cavity which its resonant frequency is approximately at the middle of the first H-polarization band gap of the basis triangular lattice. Then we obtained dipole modes and magnetic field distribution of this cavity using the Finite... 

We investigate theoretically the sheet-current density and total magnetic field (MF) distribution due to a thin, type-II superconducting annulus sample. We have supposed a washer (with the inner and outer radii a and b) carrying sub-critical currents subject to an applied magnetic field. The sample is an ideal washer with no bulk pinning, under two different situations: (a) when flux is focused into the central hole and net current flowing around the washer is zero but the external field Ha=Ba/μ is on, and (b) in the presence of a potential barrier of geometrical origin. Our calculations show that the net MF is maximum in the near-edge region and in the between is weaker than other areas.... 

New geometrical counterparts to the conventional Einzel lens, cubic, and the continuous body electrostatic (CBE) lenses are introduced and their performances are investigated in terms of different aberrations and input beam properties. Design curves for the continuous body electrostatic lens are presented. Relative sensitivity is proposed as a figure of merit, based on which the focusing characteristics of the two new lenses are compared with that of a conventional Einzel, and a quadrupole lenses of the same size, as well. Moreover, performance and characteristics of the lenses are compared in terms of their corresponding sensitivities to the applied voltage and the incidence beam... 

Electrospray technique is one of the commonly used methods for generating nanoparticles. In this method, the chemical solution which consists of a polymer and its solvent are injected into an electric field via a nozzle. At the end of this nozzle, due to electric forces, a certain part of this liquid is separated. Then, the separated part is divided into smaller particles and the solvent is evaporated and hence, the nanoparticles are acquired. Produced nanoparticales are collected in deionized water placed under the certain distant from nozzle. However, construction of this method is generally based on practical results. In this paper, modeling and performance evaluation of high voltage... 

Modified forms of WKB expansion of electromagnetic field distribution with variable coefficients are proposed for both TE and TM polarizations. Based on a method similar to the previously reported differential transfer matrix method [1,2], the analytical expressions of those aforementioned coefficients are then derived. The applicability and accuracy of the presented method are shown via some numerical examples. © 2007 EuMA  

High-temperature superconducting (HTS) transformers with multi-segment windings have been proposed in earlier literatures for the hysteresis loss reduction and short circuit electromagnetic force mitigation. The optimum distributive ratios for these multi-segment windings have been determined in earlier literatures. Asymmetrical seven segment winding with its optimum distributive ratio (k = 1/12) results in minimization of short circuit electromagnetic forces under normal tap and any adjusted tap. However, insulation design and leakage inductance calculation for the multi-segment winding of an HTS transformer have not been addressed in past literatures. Insulation design is one of the most... 

Ca-doped Ni–Mg–Mn spinel ferrites with compositions of Ni0·5Mg0·3Mn0.2CaxFe2-xO4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were prepared via sol-gel auto-ignition technique. TGA/DTA, FTIR, XRD, FESEM, and VSM were employed to evaluate the thermal, spectral, structural, morphological, and magnetic features of Ca-doped Ni–Mg–Mn spinel ferrites. TGA/DTA curves show the weight loss in the sample. This weight loss was attributed to the oxidation and decomposition of the sample contents at a temperature of 500 °C. XRD reveals a single-phase structure of the Ni–Mg–Mn nano ferrites. A single-phase orthorhombic structure was confirmed for Ca-doped Ni–Mg–Mn ferrites. Structural parameters such as lattice... 

Numerical simulation of the electrical field distribution helps in-depth understanding of the mechanisms behind the responses and the benefits of the high voltage pulse comminution. The COMSOL Multiphysics package was used to numerically simulate the effect of ore compositions in this study. Regarding phosphate ore particles shape and composition, the effects of mineral composition, particle size, particle shape and electrodes distance were investigated on the electrical field intensity and distribution. The results show that the induced electrical field is significantly dependent on the electrical properties of minerals, the feed particle size and the location of conductive minerals in... 

A large number of generators failed due to stator winding problems, mainly insulation deterioration. Insulation degradation assessment plays vital role in the asset life management. Electro thermal analysis is the main characteristic for simulation of generator behavior and to improve the design of stator slot's insulation. Dielectric parameters such as insulation thickness, spacing, material types, geometry of winding and slot are major design consideration. A very powerful method available to analyze electro thermal performance is Finite Element Method (FEM) which is used in this paper. The analysis of various stator coil and slot configurations are used to design the better dielectric... 

Numerical simulation of the electrical field distribution helps in-depth understanding of the mechanisms behind the responses and the benefits of the high voltage pulse comminution. The COMSOL Multiphysics package was used to numerically simulate the effect of ore compositions in this study. Regarding phosphate ore particles shape and composition, the effects of mineral composition, particle size, particle shape and electrodes distance were investigated on the electrical field intensity and distribution. The results show that the induced electrical field is significantly dependent on the electrical properties of minerals, the feed particle size and the location of conductive minerals in... 

Consider an arbitrarily oriented ellipsoidal domain near the interface of an isotropic bimaterial space. It is assumed that a general class of piecewise nonuniform dilatational eigenstrain field is distributed within the ellipsoidal domain. Two theorems relevant to prediction of the nature of the induced displacement field for the interior and exterior points of the ellipsoidal domain are stated and proved. As a resultant the exact analytical expression of the elastic fields are obtained rigorously. In this work a new Eshelby-like tensor, A is introduced. In particular, the closed-form expressions for A associated with the interior points of spherical and cylindrical inclusion are derived.... 

We have developed a simulation system for nanoscale high-electron mobility transistors, in which the self-consistent solution of Poisson and Schrödinger equations is obtained with the finite element method. We solve the exact set of nonlinear differential equations to obtain electron wave function, electric potential distribution, electron density, Fermi surface energy and current density distribution in the whole body of the device. For more precision, local dependence of carrier mobility on the electric field distribution is considered. We furthermore compare the simulation to a recent experimental measurement and observe perfect agreement. We also propose a novel graded channel design,... 

A new, fast, and efficient approach based on the differential transfer matrix idea, is proposed for analysis of nonuniform nonlinear distributed feedback structures. The a priori knowledge of the most-likely electromagnetic field distribution within the distributed feedback region is exploited to speculate and factor out the rapidly varying portion of the electromagnetic fields. In this fashion, the transverse electromagnetic fields are transformed into a new set of envelope functions, whereupon the numerical difficulty of solving the nonlinear coupled differential equations is partly imparted to the analytical factorization of the fields. This process renders a new set of well-behaved... 

Appealing advantages of high-temperature superconducting (HTS) transformers are very promising for the contemporary and future power delivery systems. Cryogenic insulation technology is one of the key technologies for their commercialization. In this paper insulation design of the end part of cryogenic high voltage (H. V.) bushing of a 230/20 kV HTS transformer is developed. Analytical relations and finite element method (FEM) modelling, through application of COMSOL Multiphysics software, are employed for determination of electric field distribution in this design process. Weibull 0.1% dielectric breakdown strength has been considered as criterion for insulation design. Different shape and... 

In this paper, a three-dimensional steady state incompressible turbulent air flow is considered in a large single room. The buoyancy affected turbulent air flow is numerically simulated by solving governing equations. The turbulence modeling includes both κ - ε and zero-equation models and their results are compared to the experimental data. The paper reviews several aspects, such as displacement of radiator system performance, temperature and flow field distribution and comfort conditions. The results show that the best temperature distribution and comfort condition are obtained when the radiator is installed under the window and its height is equal to or greater than that of the window. ©... 

Modified forms of WKB expansion of electromagnetic field distribution with variable coefficients are proposed for both TE and TM polarizations. Based on a method similar to the previously reported differential transfer matrix method [1,2], the analytical expressions of those aforementioned coefficients are then derived. The applicability and accuracy of the presented method are shown via some numerical examples. © 2007 EuMA  

NiZn nanoferrites doped with rare-earth cations having stoichiometric composition such as Ni0.5Zn0.5R0.02Fe1.98O4 (R = Tb, Pr, Ce, Gd, Y) were prepared by sol–gel technique. The same amount of Ni and Zn with constant ratio of different rare-earths ions were doped to investigate the variations in the properties. X-ray diffraction (XRD), Field emission electron microscope (FESEM), and vibrating sample magnetometer (VSM) were used to investigate the structure, morphology, and magnetic properties of rare-earth doped NiZn nanoferrites, respectively. X-ray density, bulk density, and porosity were also calculated. Phase, crystallite size, structure, d-spacing, lattice parameter, micro strain, and... 

NiZn nanoferrites doped with rare-earth cations having stoichiometric composition such as Ni0.5Zn0.5R0.02Fe1.98O4 (R = Tb, Pr, Ce, Gd, Y) were prepared by sol–gel technique. The same amount of Ni and Zn with constant ratio of different rare-earths ions were doped to investigate the variations in the properties. X-ray diffraction (XRD), Field emission electron microscope (FESEM), and vibrating sample magnetometer (VSM) were used to investigate the structure, morphology, and magnetic properties of rare-earth doped NiZn nanoferrites, respectively. X-ray density, bulk density, and porosity were also calculated. Phase, crystallite size, structure, d-spacing, lattice parameter, micro strain, and...