Vol. 13, No. 2, June 2016


Karl Lundengård, Milica Rančić, Vesna Javor, Sergei Silvestrov
Application of the Multi-Peaked Analytically Extended Function to Representation of Some Measured Lightning Currents
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DOI: 10.2298/SJEE160215001L
Abstract: A multi-peaked form of the analytically extended function (AEF) is used for approximation of lightning current waveforms in this paper. The AEF function’s parameters are estimated using the Marquardt least-squares method (MLSM), and the general procedure for fitting the p-peaked AEF function to a waveform with an arbitrary (finite) number of peaks is briefly described. This framework is used for obtaining parameters of 2-peaked waveforms typically present when measuring first negative stroke currents. Advantages, disadvantages and possible improve-ments of the approach are also discussed.
Keywords: Analytically extended function, Lightning discharge, Marquardt least-squares method.

Vladimir Mladenović, Danijela Milošević
A Novel-Iterative Simulation Method for Performance Analysis of Non-Coherent FSK/ASK Systems Over Rice/Rayleigh Channels using the Wolfram Language
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DOI: 10.2298/SJEE151118002M
Abstract: In this paper, a new approach in solving and analysing the performances of the digital telecommunication non-coherent FSK/ASK system in the presence of noise is derived, by using a computer algebra system. So far, most previous solutions cannot be obtained in closed form, which can be a problem for detailed analysis of complex communication systems. In this case, there is no insight into the influence of certain parameters on the performance of the system. The analysis, modelling and design can be time-consuming. One of the main reasons is that these solutions are obtained by utilising traditional numerical tools in the shape of closed-form expressions. Our results were obtained in closed-form solutions. They are resolved by the introduction of an iteration-based simulation method. The Wolfram language is used for describing applied symbolic tools, and SchematicSolver application package has been used for designing. In a new way, the probability density function and the impact of the newly introduced parameter of iteration are performed when errors are calculated. Analyses of the new method are applied to several scenarios: without fading, in the presence of Rayleigh fading, Rician fading, and in cases when the signals are correlated and uncorrelated.
Keywords: Wolfram language, Iteration-Based Simulation Method, Fading, Closed-form solution, Closed-form expression.

Mirjana T. Perić, Saša S. Ilić, Slavoljub R. Aleksić
Shielded Coupled Multilayered Microstrip Lines Analysis using HBEM
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DOI: 10.2298/SJEE160217003P
Abstract: Shielded symmetrical coupled multilayered microstrip lines analysis have been done using the hybrid boundary element method (HBEM), which is developed a few years ago at the Faculty of Electronic Engineering in Niš. The quasi-TEM approximation is applied. Influences of different parameters as well as dimensions of such microstrip lines on characteristic parameters distribution are investigated. The results are presented in graphs and tables. In order to verify the obtained results, some comparative results are shown. The authors found them to be in very good agreement with the HBEM results.
Keywords: Characteristic parameters, Finite element method, Hybrid boundary element method, Multilayered structures, Shielded coupled microstrip lines.

Tangella Bhavani Shanker, Hebbale Narasimhaiah Nagamani, Gururaj Sudhindra Punekar
Acoustic Emission Partial Discharge Detection Technique Applied to Fault Diagnosis: Case Studies of Generator Transformers
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DOI: 10.2298/SJEE160223004S
Abstract: In power transformers, locating the partial discharge (PD) source is as important as identifying it. Acoustic Emission (AE) sensing offers a good solution for both PD detection and PD source location identification. In this paper the principle of the AE technique, along with in-situ findings of the online acoustic emission signals captured from partial discharges on a number of Generator Transformers (GT), is discussed. Of the two cases discussed, the first deals with Acoustic Emission Partial Discharge (AEPD) tests on two identical transformers, and the second deals with the AEPD measurement of a transformer carried out on different occasions (years). These transformers are from a hydropower station and a thermal power station in India. Tests conducted in identical transformers give the provision for comparing AE signal amplitudes from the two transformers. These case studies also help in comprehending the efficacy of integrating Dissolved Gas is (DGA) data with AEPD test results in detecting and locating the PD source.
Keywords: Acoustic Emission, Condition Monitoring, Dissolved Gas is, Partial Discharge, Transformer.

El-Sayed Mohamed El-Sayed Zayed, Abdul-Ghani Al-Nowehy
Exact Traveling Wave Solutions for Nonlinear PDEs in Mathematical Physics using the Generalized Kudryashov Method
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DOI: 10.2298/SJEE1602203M
Abstract: The generalized Kudryashov method is applied in this article for finding the exact solutions of nonlinear partial differential equations (PDEs) in mathematical physics. Solitons and other solutions are given. To illustrate the validity of this method, we apply it to three nonlinear PDEs, namely, the diffusive predator-prey system, the nonlinear Bogoyavlenskii equations and the nonlinear telegraph equation. These equations are related to signal analysis for transmission and propagation of electrical signals. As a result, many analytical exact solutions of these equations are obtained including symmetrical Fibonacci function solutions and hyperbolic function solutions. Physical explanations for some solutions of the given three nonlinear PDEs are obtained. Comparison our new results with the well-known results are given.
Keywords: Nonlinear PDEs, Generalized Kudryashov method, Symmetrical hyperbolic Fibonacci function, Exact solutions, The diffusive predator-prey system, The nonlinear Bogoyavlenskii equations, The nonlinear telegraph equation.

Adel Bendjerad, Sebti Boukhtache1, Abdelhamid Benhaya, Dominique Luneau, Seddik El Hak Abaidia, Kaddour Benyahia
Modeling of Magnetic Properties of Iron Thin Films Deposited by RF Magnetron Sputtering using Preisach Model
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DOI: 10.2298/SJEE1602229B
Abstract: Iron thin films were deposited on glass substrates using RF magnetron sputtering and their optimal deposition conditions were determined. The structure properties were analyzed using x-ray diffraction (XRD) and their magnetic hysteresis loops were obtained by Vibrating Sample Magnetometer (VSM) at room temperature. In this situation, the magnetic field is either parallel or perpendicular to the substrate plane. The main contribution of this work is to characterize the thin layers and present a mathematical model that can get best fit of the characteristics B(H). By using Preisach model, good agreement was obtained between theoretical and experimental results in both cases.
Keywords: Iron (Fe), RF magnetron, thin layer, XRD, VSM, Hysteresis, Preisach model.

Saradindu Ghosh, Pratap Kumar Panigrahi, Dayal R. Parhi
Performance Comparison of Novel WNN Approach with RBFNN in Navigation of Autonomous Mobile Robotic Agent
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DOI: 10.2298/SJEE1602239G
Abstract: This paper addresses the performance comparison of Radial Basis Function Neural Network (RBFNN) with novel Wavelet Neural Network (WNN) of designing intelligent controllers for path planning of mobile robot in an unknown environment. In the proposed WNN, different types of activation functions such as Mexican Hat, Gaussian and Morlet wavelet functions are used in the hidden nodes. The neural networks are trained by an intelligent supervised learning technique so that the robot makes a collision-free path in the unknown environment during navigation from different starting points to targets/goals. The efficiency of two algorithms is compared using some MATLAB simulations and experimental setup with Arduino Mega 2560 microcontroller in terms of path length and time taken to reach the target as an indicator for the accuracy of the network models.
Keywords: Autonomous Navigation, Collision Avoidance, Radial Basis Function Neural Network, Wavelet Neural Network.

Sengathir Janakiraman, Manoharan Rajendiran
An Erlang Factor-Based Conditional Reliability Mechanism for Enforcing Co-operation in MANETs
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DOI: 10.2298/SJEE1602265J
Abstract: Reputation is considered to be one of the vital entities for maintaining collaboration among wireless mobile nodes present in an ad hoc environment. The nodes in MANET are dynamic and could change its behaviour drastically, but establishing maximum level of cooperation between these nodes is highly crucial. Moreover, the presence of selfish nodes has a greater impact on the resilience of the network. Hence, a need arises for formulating a mechanism that deals with these selfish nodes. In this paper, we contribute an Erlang distribution based Conditional Reliability Mechanism (ECRCM) that aids in detecting and isolating the selfish nodes present in an ad hoc environment. This mathematical model makes the routing decision with the help of a parameter called Erlang factor based Conditional Reliability Coefficient (ECRC) determined for each and every mobile node present in the ad hoc network. Extensive simulations were carried out through ns-2 simulator and the analysis was based on performance metrics such as packet delivery ratio, throughput, control overhead and total overhead. ECRCM also helps in framing an optimal threshold range for selfish node detection. From the results, it is obvious that the threshold range derived in our study remarkably identifies maximum number of selfish nodes when compared to the selfishness detecting parameters available in the literature.
Keywords: Erlang based Conditional Reliability Coefficient, Selfish nodes, Probability of genuineness, Network Resilience, Optimal threshold range, Exponential distribution.

Olga Ristić, Bratislav D. Iričanin, Vladica Mijailović
Dynamic Modeling and Simulation of Power Transformer Maintenance Costs
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DOI: 10.2298/SJEE1602289R
Abstract: The paper presents the dynamic model of maintenance costs of the power transformer functional components. Reliability is modeled combining the exponential and Weibull's distribution. The simulation was performed with the aim of corrective maintenance and installation of the continuous monitoring system of the most critical components. Simulation Dynamic System (SDS) method and VENSIM PLE software was used to simulate the cost. In this way, significant savings in maintenance costs will be achieved with a small initial investment.
Keywords: Modeling, Exponential and Weibull's distribution, Simulation, Power transformer, Maintenance.

©2016 Serbian Journal of Electrical Engineering