Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411

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Citation - WoS: 9
Citation - Scopus: 14
A Machine Learning Study to Enhance Project Cost Forecasting
(Elsevier, 2022) Inan, Tolga; İnan, Tolga; Narbaev, Timur; Hazir, Oncu; Elektrik-Elektronik Mühendisliği
In project management it is critical to obtain accurate cost forecasts using effective methods. This study presents a Machine Learning model based on Long-Short Term Memory to forecast the project cost. The model uses the seven-dimensional feature vector, including schedule and cost performance factors and their moving averages as a predictor. Based on the cost variation patterns from the training phase, we validate the model using three hundred experiments in the testing phase. Overall, the proposed model produces more accurate cost estimates when compared to the traditional Earned Value Management index-based model. Copyright (C) 2022 The Authors.
Citation - WoS: 0
Citation - Scopus: 0
A novel method to solve 2nd order neumann type boundary value problems in electrostatics
(Applied Computational Electromagnetics Soc, 2017) Sener, Goker; Şener, Göker; 17740; Elektrik-Elektronik Mühendisliği
In this paper, the numerical method of nonpolynomial spline approximation is used to solve 2nd order Neumann type boundary value problems (bvp's) in electrostatics. This new approach provides more accurate results than the polynomial approximations and the spectral methods. The literature contains very little on the solution of Neumann type bvp's because of the fact that a unique solution does not exist for all problems. In electrostatics, Neumann type bvp's are encountered for finding the electrostatic potential inside closed surfaces where the normal derivative of the electric potential is specified everywhere on the surface. Two examples are presented to prove the accuracy of the proposed method. In these examples, the governing differential equation is solved to find the electrostatic potential inside a region bounded by conductors that are maintained at constant voltages. The results are compared with the analytic solutions.
Citation - WoS: 2
Citation - Scopus: 5
A Novel Transformerless Single-Phase Three-Level Buck-Boost Inverter
(Ieee, 2023) Demirkutlu, Eyyup; Iskender, Ires; 133746
This paper proposes a novel transformerless, single-phase, three-level, buck-boost inverter. The proposed inverter can suppress the leakage current drawn from the input power source and provide a long-lasting solution for applications with a wide range and unregulated input voltage. Unlike similar topologies, in the proposed inverter there is no need to have a mid-point of DC sources or DC bus capacitors at the input side of the inverter. A single-phase, three-level, buck-boost inverter for realizing the power stage with 110-Vrms output AC voltage and a range of 100V-200V input DC voltage is investigated in this study. The proposed topology has been proven through theory, computer simulations, and experimental studies with SiC MOSFETs-based prototype of a 300-VA power supply. Theory, computer simulation, and experimental results are all correlated.
Citation - WoS: 7
Citation - Scopus: 8
Anisotropy effect on performance of subcarrier intensity modulated binary phase shift keying optical wireless communication links in weakly turbulent underwater channel
(Taylor & Francis Ltd, 2019) Baykal, Yahya; Gökçe, Muhsin Caner; Gokce, Muhsin C.; Ata, Yalcin; 7812; Elektronik ve Haberleşme Mühendisliği
The effect of the anisotropy on the bit-error-rate (BER) performance of subcarrier intensity modulated (SIM) binary phase shift keying (BPSK) optical wireless communication (OWC) links operating in weakly turbulent underwater channels is examined. BER variations versus the anisotropic factor are examined when the bandwidth, photodetector responsivity, load resistor and the underwater turbulence parameters are varied. As anisotropy in the underwater channel becomes larger, SIM BPSK OWC links have better BER performance at any link and turbulence parameter.
Citation - WoS: 1
Citation - Scopus: 1
Antenna Synthesis by Levin's Method using a Novel Optimization Algorithm for Knot Placement
(Applied Computational Electromagnetics Soc, 2023) Sener, Goker; Şener, Göker; 17740; Elektrik-Elektronik Mühendisliği
- Antenna synthesis refers to determining the antenna current distribution by evaluating the inverse Fourier integral of its radiation pattern. Since this inte-gral is highly oscillatory, Levin's method can be used for the solution, providing high accuracy. In Levin's method, the integration domain is divided into equally spaced sub-intervals, and the integrals are solved by transfer-ring them into differential equations. This article uses a new optimization algorithm to determine the location of these interval points (knots) to improve the method's accuracy. Two different antenna design examples are pre-sented to validate the accuracy and efficiency of the pro-posed method for antenna synthesis applications.
Citation - WoS: 0
Citation - Scopus: 0
Antenna Synthesis by Levin’s Method using Reproducing Kernel Functions
(Applied Computational Electromagnetics Soc, 2023) Sener, Goker; Şener, Göker; 17740; Elektrik-Elektronik Mühendisliği
An antenna synthesis application is presented by solving a highly oscillatory Fourier integral using a stable and accurate Levin's algorithm. In antenna synthesis, the current distribution is obtained by the inverse Fourier integral of the antenna radiation pattern. Since this integral is highly oscillatory, the Levin method can be used for its solution. However, when the number of nodes or the frequency increases, the Levin method becomes unstable and ineffective due to the large condition number of the interpolation matrix. Thus, an improved scheme of the method is used in an antenna synthesis application in which reproducing kernel functions are used as the basis of the approximation function. The accuracy of the new method is verified by a log-periodic antenna example. The error and stability analysis results show that the new method is more stable and accurate than other well-known kernels, especially for a large number of nodes.
Citation - WoS: 24
Citation - Scopus: 24
Aperture averaging in multiple-input single-output free-space optical systems
(Optical Soc Amer, 2016) Gokce, Muhsin Caner; Gökçe, Muhsin Caner; Baykal, Yahya; Uysal, Murat; 28643; 7812; 124615; Elektronik ve Haberleşme Mühendisliği
Multiple-input single-output (MISO) techniques are employed in free-space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, for the MISO FSO system, a partially coherent radial array and a finite-sized receiver aperture are used at the transmitter and the receiver, respectively. Using the extended Huygens - Fresnel principle, we formulate the average power and the power correlation at the finite-sized slow detector in weak atmospheric turbulence. System performance indicators such as the power scintillation index and the aperture averaging factor are determined. Effects of the source size, ring radius, receiver aperture radius, link distance, and structure constant and the degree of source coherence are analyzed on the performance of the MISO FSO system. In the limiting cases, the numerical results are found to be the same when compared to the existing coherent and partially coherent Gaussian beam scintillation indices. (C) 2016 Optical Society of America
Citation - WoS: 8
Citation - Scopus: 9
Aperture averaging in multiple-input single-output free-space optical systems
(Spie-soc Photo-optical instrumentation Engineers, 2015) Gokce, Muhsin C.; Gökçe, Muhsin Caner; Baykal, Yahya; Kamacioglu, Canan; Uysal, Murat; 28643; 7812; 124615; Elektronik ve Haberleşme Mühendisliği
Multiple-input single-output systems are employed in free-space optical links to mitigate the degrading effects of atmospheric turbulence. We formulate the power scintillation as a function of transmitter and receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens Fresnel principle. Then the effect of the receiver aperture averaging is quantified. To get consistent results, parameters are chosen within the range of validity of the wave structure functions. Radial array beams and a Gaussian weighting aperture function are used at the transmitter and the receiver, respectively. It is observed that the power scintillation decreases when the source size, the ring radius, the receiver aperture radius, and the number of array beamlet increase. However, increasing the number of array beamlets to more than three seems to have negligible effect on the power scintillation. It is further observed that the aperture averaging effect is stronger when radial array beams are employed instead of a single Gaussian beam. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 6
Citation - Scopus: 10
Application of adaptive optics on bit error rate of M-ary pulse-position-modulated oceanic optical wireless communication systems
(Iop Publishing Ltd, 2020) Baykal, Yahya; Gökçe, Muhsin Caner; Gokce, Muhsin C.; Ata, Yalcin; 7812; Elektronik ve Haberleşme Mühendisliği
An adaptive optics correction arising from the sum of tilt, focus, astigmatism and coma components is applied to the bit error rate (BER) of M-ary pulse-position-modulated (PPM) oceanic optical wireless communication systems. The percentage reduction in BER is evaluated versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and that of kinetic energy per unit mass of fluid under different data bit rates, avalanche photodiode (APD) average current gains and the M values of the M-ary PPM. Our findings indicate that the percentage reduction in BER becomes larger when the ratio of temperature to salinity contributions to the refractive index spectrum or the rate of dissipation of mean-squared temperature or the data bit rate or the M value of the M-ary PPM is smaller, and when the rate of dissipation of kinetic energy per unit mass of fluid or the APD average current gain is larger.
Citation - WoS: 29
Citation - Scopus: 35
BER evaluations for multimode beams in underwater turbulence
(Taylor & Francis Ltd, 2016) Arpali, Serap Altay; Baykal, Yahya; Arpali, Caglar; 7812
In underwater optical communication links, bit error rate (BER) is an important performance criterion. For this purpose, the effects of oceanic turbulence on multimode laser beam incidences are studied and compared in terms of average BER (< BER >), which is related to the scintillation index. Based on the log-normal distribution, < BER > is analysed for underwater turbulence parameters, including the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, the parameter that determines the relative strength of temperature and salinity in driving index fluctuations, the Kolmogorov microscale length and other link parameters such as link length, wavelength and laser source size. It is shown that use of multimode improves the system performance of optical wireless communication systems operating in an underwater medium. For all the investigated multimode beams, decreasing link length, source size, the relative strength of temperature and salinity in driving the index fluctuations, the rate of dissipation of the mean squared temperature and Kolmogorov microscale length improve the < BER >. Moreover, lower < BER > values are obtained for the increasing wavelength of operation and the rate of dissipation of the turbulent kinetic energy in underwater turbulence.
Citation - WoS: 30
Citation - Scopus: 31
Bit error rate of pulse position modulated optical wireless communication links in oceanic turbulence
(Optical Soc Amer, 2018) Baykal, Yahya; 7812
The upper bound of the average bit error rate (BER) of a pulse position modulated (PPM) optical wireless communication (OWC) link operating in oceanic turbulence is formulated. BER variations against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, and the rate of dissipation of kinetic energy per unit mass of fluid are found at various data bit rates, average current gains of the avalanche photodiode (APD), and M values of the M-ary PPM. It is found that under any oceanic turbulence parameters, BER performance of the PPM OWC system becomes favorable at smaller data bit rates, M values, and at larger average current gains of APD. (c) 2018 Optical Society of America
Citation - WoS: 2
Citation - Scopus: 2
Bit-error-rate performance of optical wireless system using higher order mode laser in anisotropic non-Kolmogorov turbulence
(Spie-soc Photo-optical instrumentation Engineers, 2018) Ata, Yalcin; Baykal, Yahya; 7812
The average bit-error-rate, (BER), of optical wireless system using higher order mode laser beam is investigated when atmospheric turbulence shows anisotropic and non-Kolmogorov characteristics. Results reveal that increase in anisotropy in both x- and y-directions positively affects the optical wireless systems performance. Increase in the beam order results in an increase in (BER) for any anisotropy level, and thus, higher order beams adversely affect the optical wireless systems performance. Larger structure constant, beam source size, and propagation distance result in larger (BER), but larger wavelength, inner scale length, and signal-tonoise ratio tend to reduce (BER). Increase in the power-law exponent of non-Kolmogorov turbulent spectrum first increases the (BER) until a certain value, and then (BER) starts to decrease when the power-law exponent is further increased. Adverse effect of higher order laser beam holds to be valid for any power-law exponent of non-Kolimogorov turbulence. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - Scopus: 0
Calculation of the Halfwidth and the Activation Energy for the Soft Raman Modes in the Brominated Compounds of Tris-Sarcosine Calcium Chloride
(Walailak University, 2022) Kiraci, A.; Kiracı, Ali; 42475; Ortak Dersler Bölümü
This letter contributes how to calculate the anomalous behavior for the damping constant (halfwidth) of the ferroelectric Tris-Sarcosine Calcium Chloride (TSSC) and its brominated compounds TSSC1−xBrx (x = 0.13, 0.42 and 0.60) from the wavenumber data of the soft modes below the phase transition temperature of TC. The pseudospin-phonon coupled (PS) and the energy fluctuation (EF) models derived from the dynamical Ising model were used. Both PS and EF models have been used to contribute understanding the temperature dependence of the phase transition mechanism of TSSC1−xBrx. In addition, values of the activation energy for TSSC1−xBrx (x = 0, 0.13, 0.42 and 0.60) were extracted from the damping constant as calculated from both models (PS and EF). Our results indicate order-disorder type phase transition for TSSC1−xBrx. © 2022, Walailak University. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 3
CASE STUDY ON THERMAL OPTIMIZATION OF OIL IMMERSED TRANSFORMER USED IN SOLAR POWER PLANT BASED ON GENETIC ALGORITHM AND COMPUTATIONAL FLUID DYNAMICS
(Vinca inst Nuclear Sci, 2023) Yukselen, Emir; İskender, İres; Iskender, Ires; 133746; Elektrik-Elektronik Mühendisliği
Transformers are one of the most capital investments in the solar power generation. Their safe and stable operations in the electrical networks are important. The main failure factor of transformers is the high temperature generated by the losses during operation, which increases the probability of insulation damage that significantly affects the useful life of transformer. Considering the importance of oil temperature and its effects on the life of the transformer, a numerical method is developed in this paper to optimize the cooling system of the transformer. In this regard, genetic algorithm is used as an optimization method to minimize the total cost of the cooling system while maintaining the required thermal conditions of the transformer. A comprehensive parametric study is carried out among the effective cooling geometry parameters using 3-D electromagnetic and thermal models of the photovoltaic transformer to evaluate and analyze the temperature distribution. The accuracy and feasibility of the proposed method is established by comparing the numerical results with those obtained from the experimental test. The results of the proposed method are found to be in a good agreement with the experimental and simulation results.
Citation - Scopus: 4
Comparing control performances of mrac and pid applied on a brushless dc motor
(International Organization on 'Technical and Physical Problems of Engineering', 2020) Ciba, S.; İskender, İres; Iskender, I.; Ariani, H.A.; 133746; Elektrik-Elektronik Mühendisliği
Brushless DC motors are powered by a DC electric source and are used widely used in appliance, automotive, aerospace, medical and industrial equipment due to their compact size and light weight. Parallel to improvements in semiconductor industries the operating frequency of semiconductor switches and microcontrollers are getting improve and this provides conditions to use different algorithms in motor control. In this study the reference model adaptive control of a DC brushless motor will be studied. Brushless DC motors have some advantages such as long working life, high efficiency, and low maintenance requirements; however their control is a bit complicated. For this reason, there have been published many studies in relative with speed control of brushless DC motors. Classical or modern control methods can be used for this purpose. In this study, BLDC motor is controlled with firstly classical PID controller and secondly model reference adaptive control (MRAC) based on MIT law method and the results are compared. © 2020, International Organization on 'Technical and Physical Problems of Engineering'. All rights reserved.
Citation - WoS: 83
Citation - Scopus: 83
Correlation and structure functions of Hermite-sinusoidal-Gaussian laser beams in a turbulent atmosphere
(Optical Soc Amer, 2004) Baykal, Y
To study the performance of atmospheric optical links by using Hermite-sinusoidal-Gaussian laser beam sources, we derive the log-amplitude and the phase correlation and structure functions of such beams in a turbulent atmosphere. Our formulations correctly reduce to the known higher-order mode correlation and structure functions, which in turn reduce to the fundamental-mode (TEM00-mode) results. Several special cases of our formulation are presented, among which the case involving Hermite-cosh-Gaussian dependence is especially noted, since this case is of interest to us owing to the nature of cosh dependence exhibiting the concentration of the energy in the outer lobes of the beam. (C) 2004 Optical Society of America.
Citation - WoS: 4
Citation - Scopus: 5
Correlation of multimode fields in atmospheric turbulence
(Optica Publishing Group, 2023) Baykal, Yahya; Gökçe, Muhsin Caner; Gokce, Muhsin Caner; Ata, Yalcin; Gercekcioglu, Hamza; 7812; Elektronik ve Haberleşme Mühendisliği
Multimode field correlations are evaluated in atmospheric turbulence. High order field correlations are special cases of the results that we obtained in this paper. Field correlations are presented for various numbers of mul- timodes, various multimode contents of the same number of modes, and various high order modes versus the diagonal distance from various receiver points, source size, link length, structure constant, and the wavelength. Our results will be of help especially in the design of heterodyne systems operating in turbulent atmosphere and fiber coupling efficiency in systems employing multimode excitation.(c) 2023 Optica Publishing Group
Citation - WoS: 2
Citation - Scopus: 2
Correlations of multimode optical incidences in a turbulent biological tissue
(Optica Publishing Group, 2023) Baykal, Yahya; Gökçe, Muhsin Caner; Gokce, Muhsin Caner; Gerekcioglu, Hamza; Ata, Yalin; 7812; Elektronik ve Haberleşme Mühendisliği
In a turbulent biological tissue, field correlations at the observation plane are found when a multimode optical incidence is used. For different multimode structures, variations of the multimode field correlations are evaluated against the biological tissue turbulence parameters, i.e., the strength coefficient of the refractive-index fluctuations, fractal dimension, characteristic length of heterogeneity, and the small length-scale factor. Using a chosen multimode content, for specific biological tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human), and deep dermis (mouse), field correlations are evaluated versus the strength coefficient of the refractive-index fluctuations and small length-scale factor. Again, with a chosen multimode content, behavior of the field correlations is studied against the strength coefficient of the refractive-index fluctuations for various diagonal lengths and the transverse coordinate at the observation plane. Finally, the field correlation versus the strength coefficient of the refractive-index fluctuations is reported for different single modes, which are special cases of multimode excitation. This topic is being reported in the literature for the first time, to our knowledge, and the presented results can be employed in many important biological tissue applications. (c) 2023 Optica Publishing
Citation - Scopus: 0
Cost optimization of oil type distribution transformer using multi-objective genetic algorithm
(Erol Kurt, 2024) Telli, S.; İskender, İres; Iskender, I.; Yükselen, E.; 133746; Elektrik-Elektronik Mühendisliği
The demand for electrical energy is increasing day by day with the development of technology in the world. Distributing electric energy to all regions that need energy is a principal issue, and this necessitates the use of transformers to convert the voltage to the desired level. Accordingly, the use of transformers, one of the electrical devices converting AC voltage level at a defined frequency has grown significantly. In this study, design parameters of a 25 kVA, 33/0.4 kV, Yzn11, oil-type distribution transformer are optimized using the Multi-Objective Genetic Algorithm (MOGA) technique by decreasing the weight of the significant materials and manufacturing cost. Electromagnetic analysis of the transformer is performed with ANSYS Maxwell based on the design results obtained from the optimization study for validation of the method. The experimental design parameters are also compared with the optimization results. It is observed that optimum results are achieved by using the proposed approach. © 2024 Published by peer-reviewed open access scientific journal, JES at DergiPark (https://dergipark.org.tr/jes)
Citation - WoS: 10
Citation - Scopus: 10
Cross-beam scintillations in underwater medium
(Spie-soc Photo-optical instrumentation Engineers, 2016) Baykal, Yahya; 7812
The fluctuation in the intensity, which is quantified by the scintillation index, is evaluated for cross beams when such beams propagate in an underwater medium experiencing turbulence. The variations in the scintillation index are investigated against the changes in the size of the cross beams, the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, and the rate of dissipation of kinetic energy per unit mass of fluid. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

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