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Nigde, Turkey

Niğde University is a public higher educational institution located in Niğde, Central Anatolia in Turkey. It has five faculties, two institutes, two colleges and six vocational colleges. The university campus is situated 6 km southwest of Niğde. Wikipedia.

Donmez O.,Nigde University
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present the numerical study of dynamical instability of a pressure-supported relativistic torus, rotating around the black hole with a constant specific angular momentum on a fixed space-time background, in case of perturbation by a matter coming from the outer boundary. Two-dimensional hydrodynamical equations are solved at equatorial plane using the high resolution shock capturing method to study the effect of perturbation on the stable systems. We have found that the perturbed torus creates an instability which causes the gas falling into the black hole in a certain dynamical time. All the models indicate an oscillating torus with certain frequency around their instant equilibrium. The dynamic of the accreted torus varies with the size of initial stable torus, black hole spin and other variables, such as Mach number, sound speed, cusp location of the torus, etc. The mass accretion rate is slightly proportional to the torus-to-hole mass ratio in the black hole-torus system, but it strongly depends on the cusp location of the torus. The cusp located in the equipotential surfaces of the effective potential moves outwards into the torus. The dynamical change of the torus increases the mass accretion rate and triggers the Papaloizou-Pringle instability. It is also observed that the growth of the m = 1 mode of the Papaloizou-Pringle instability occurs for a wide range of fluid and hydrodynamical parameters and a black hole spin. We have also computed the quasi-periodic oscillations from the oscillating relativistic torus. © 2013 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Barut M.,Nigde University
Energy Conversion and Management | Year: 2010

This study offers a novel extended Kalman filter (EKF) based estimation technique for the solution of the on-line estimation problem related to uncertainties in the stator and rotor resistances inherent to the speed-sensorless high efficiency control of induction motors (IMs) in the wide speed range as well as extending the limited number of states and parameter estimations possible with a conventional single EKF algorithm. For this aim, the introduced estimation technique in this work utilizes a single EKF algorithm with the consecutive execution of two inputs derived from the two individual extended IM models based on the stator resistance and rotor resistance estimation, differently from the other approaches in past studies, which require two separate EKF algorithms operating in a switching or braided manner; thus, it has superiority over the previous EKF schemes in this regard. The proposed EKF based estimation technique performing the on-line estimations of the stator currents, the rotor flux, the rotor angular velocity, and the load torque involving the viscous friction term together with the rotor and stator resistance is also used in the combination with the speed-sensorless direct vector control of IM and tested with simulations under the challenging 12 scenarios generated instantaneously via step and/or linear variations of the velocity reference, the load torque, the stator resistance, and the rotor resistance in the range of high and zero speed, assuming that the measured stator phase currents and voltages are available. Even under those variations, the performance of the speed-sensorless direct vector control system established on the novel EKF based estimation technique is observed to be quite good. © 2010 Elsevier Ltd. All rights reserved. Source

Aydin E.,Nigde University
Journal of Constructional Steel Research | Year: 2012

A new damper optimization method for finding optimal size and location of the added viscous dampers is proposed based on the elastic base moment in planar steel building frames. A Fourier Transform is applied to the equation of the motion and the transfer function in terms of the fundamental natural frequency of the structures is defined. The transfer function amplitude of the elastic base moment evaluated at the first natural circular frequency of the structure is chosen as a new objective function in the minimization problem. The damper coefficients of the added viscous dampers are taken into consideration as design variables in a steel planar building frame. The transfer function amplitude of the elastic base moment is minimized under an active constraint on the sum of the damper coefficients of the added dampers and the passive constraints on the upper and lower bounds of the added dampers. The optimal damper design presented in this paper is compared with other optimal damper methods based on top displacement, top absolute acceleration and base shear. A ten-storey steel planar building frame is chosen to be rehabilitated with the optimal dampers. The optimal damper allocation is obtained for the transfer function amplitude of the elastic base moment then compared with the other damper optimization methods in terms of the transfer function response. The results of the proposed method show that the method can also be beneficial to decrease both the base moment and the interstorey drift ratios in some frequency regions. © 2012 Elsevier Ltd. All rights reserved. Source

Gungor A.,Nigde University
International Journal of Hydrogen Energy | Year: 2011

In this study, effects of the operational parameters such as gasifier temperature, bed operational velocity, equivalence ratio, biomass particle size and biomass-to-steam ratio on hydrogen production from an atmospheric biomass FB gasifier is simulated by presently developed model. The model is one-dimensional, isothermal and steady state, and the fluid-dynamics are based on the two-phase theory of fluidization. Tar conversion is taken into account in the model. The model simulation results are also compared with and validated against experimental data given in the literature. As a result of this study, it is observed that H2 composition increased remarkably with the rise of the gasifier temperature. Small biomass particles improves H2 composition. It is unfeasible to apply too small or too large ER in biomass air-steam gasification. The increases in the mole fractions of H2 with increases in the steam flow rate indicated that the gas shift reaction has a substantial effect in air-steam gasification. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

Saridemir M.,Nigde University
Construction and Building Materials | Year: 2013

This paper presents the results of experimental study on compressive strength and secant modulus of elasticity of high strength concrete (HSC) containing different levels of silica fume, ground pumice and silica fume together with ground pumice. Three concrete series with water-binder ratios of 0.25 and a constant total binder content of 450 kg/m3 were designed. The compressive strength and secant modulus of elasticity of these concrete series were determined. The experimental results clearly reveal the use of silica fume and silica fume together with ground pumice with a very low water-binder ratio in the production of HSC. The highest compressive strength and secant modulus of elasticity are obtained in the concrete mixtures containing 15% silica fume and 15% silica fume together with 5% ground pumice. The relationship between the compressive strength and secant modulus of elasticity of HSC was also discussed. New two equations for modulus of elasticity of concrete containing different levels of silica fume, ground pumice and silica fume together with ground pumice have been proposed. The experimental results of dependent modulus of elasticity of concrete were compared with the results of various equations proposed by some of national building codes and the authors, and also the results of new equations proposed in this study. © 2013 Elsevier B.V. All rights reserved. Source

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