University of Pristina in Kosovska Mitrovica

Kosovska Mitrovica, Serbia

University of Pristina in Kosovska Mitrovica

Kosovska Mitrovica, Serbia
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Klimenta D.,University of Pristina in Kosovska Mitrovica
Heat Transfer Research | Year: 2017

The main purpose of this paper is to propose a procedure for modeling heat transfer by natural convection for both laminar and turbulent flows around an evacuated tube collector at inclination angles of 0-90o. Using the experimental results obtained by Heo and Chung (2012) for different cylinders and inclinations, the heat transfer correlations based on the fundamental dimensionless number for natural convection have been derived. Their experiments included measurements for solid circular cylinders having diameters of 0.01, 0.034, and 0.067 m, and lengths of 0.1, 0.25, and 0.45 m, as well as for a Prandtl number of 2094 in either laminar or turbulent conditions. Introducing the correlations based on the fundamental dimensionless number for natural convection, the studies performed on inclined cylinders were generalized for the whole range of Prandtl numbers. A modified Nusselt number, which represents the mean of the heat transfer correlations based on the cylinder diameter and on the cylinder length, was introduced and applied to estimate the heat transfer coefficients for natural convection on the outer surface of an evacuated tube collector surrounded by air. The results obtained by applying the proposed correlations were also compared to the results obtained using existing ones for various Prandtl numbers. © 2017 by Begell House, Inc.

Klimenta D.O.,Aalto University | Klimenta D.O.,University of Pristina in Kosovska Mitrovica | Hannukainen A.,Aalto University
Thermal Science | Year: 2017

Compared to a number of other existing correlations for heat transfer, the empirical correlations for forced convection from a short horizontal cylinder in axial air-flows usually do not involve the effects of changes in air-flow velocity and/or air-flow turbulence. Therefore, a common analysis of the heat transfer by using only one energy balance equation for entire outer surface of a solid is considered insufficient for induction motor applications because it fails to include aforementioned effects. This paper presents a novel, empirically-based methodology to estimate approximately the values of air-flow velocities and turbulence factors, that is, velocity profiles and turbulence factor models for stationary horizontal cylinders with and without fins (frame and two end-shields) in axial air-flows. These velocity profiles and turbulence factor models can then be used in analytical modelling of steady-state heat transfer from the exterior of totally enclosed fan-cooled induction motors. © 2017 Society of Thermal Engineers of Serbia.

Lekic J.,University of Pristina in Kosovska Mitrovica | Milicev D.,University of Belgrade
MODELSWARD 2015 - 3rd International Conference on Model-Driven Engineering and Software Development, Proceedings | Year: 2015

α-algorithm is able to discover a large class of workflow (WF) nets based on the behavior recorded in event logs, with the main limiting assumption that the event log is complete. Our research has been aimed at finding ways of business process models discovering based on examples of traces, i.e., logs of workflow actions that do not meet the requirement of completeness. In this aim, we have modified the existing and introduced a new relation between activities recorded in the event log, which has led to a partial correction of the process models discovering techniques, including the α-algorithm. We have also introduced the notions of causally and weakly complete logs, from which our modified algorithm can produce the same result as the original algorithm from complete logs. The effect of these modifications on the speed of the process model discovering is mostly evident for business processes in which many activities can be performed in parallel. Therefore, this paper presents preliminary results obtained from the investigation of opportunities to discover models of parallel processes based on incomplete event logs. Copyright © 2015 SCITEPRESS - Science and Technology Publications.

Radosavljevic J.,University of Pristina in Kosovska Mitrovica | Jevtic M.,University of Pristina in Kosovska Mitrovica
IET Generation, Transmission and Distribution | Year: 2016

This study presents a hybrid gravitational search algorithm-sequential quadratic programming (GSA-SQP) algorithm based on the GSAand SQP to optimal coordination of directional overcurrent relays (DOCRs). The SQP routine is incorporated in GSA as a local search mechanism to improve the performance of the conventional GSA algorithm. The coordination between DOCRs is formulated as a non-linear and highly constrained optimisation problem in which two settings namely time dial setting and pick up current setting of each relay are considered as decision variables. The main objective is to minimise the sum of operating times of all the primary relays, which are expected to operate in order to clear the faults of their corresponding zones. Performance of this approach is studied and evaluated on three different test systems with 6, 24 and 38 relays. Simulation results show that the proposed approach provides effective and robust high-quality solution of the problem. © The Institution of Engineering and Technology 2016.

Radosavljevic J.,University of Pristina in Kosovska Mitrovica | Klimenta D.,University of Pristina in Kosovska Mitrovica | Jevtic M.,University of Pristina in Kosovska Mitrovica
Journal of Electrical Engineering | Year: 2012

This paper proposed a multi-objective genetic algorithm (MOGA) based approach for determining the steady-state performance characteristics of three-phase self-excited induction generators (SEIGs) operating in parallel and supplying an unbalanced load. The symmetrical component theory is used for the transformation of a complex three- phase generatorscapacitances- load system to a simple equivalent circuit. The MOGA has been employed for the determination of unknown variables by minimizing the impedance module of the equivalent circuit. Using this approach, effects of various parameters on the terminal voltage control characteristics are examined for two parallel SEIGs with C2C connection under a single phase load. © 2012.

Djurdjevic D.Z.,University of Pristina in Kosovska Mitrovica
Proceedings of the 24th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2011 | Year: 2011

This paper is aimed at analysing the status and perspectives of the solar photovoltaic (PV) power engineering in the Republic of Serbia under present circumstances. The main objective of this paper is to assess the potential for solar PV power system utilization in Serbia. At the moment solar PV technology is not implemented in the Serbian renewable energy sources (RES) sector, however, some firm positive steps in this direction are recently taken. The effects of recently introduced feed-in tariffs (FITs) in Serbia are discussed, from the point of view of solar PVs utilization. The Serbian authorities are addressed to make an efficient policy which can enable competitive investment and utilization of emerging solar PV power systems. Assessments, calculated data and suggestions presented in this paper can be helpful to everyone who wants to participate in developing and investing in solar PV technology in Serbia. The aim of this paper is to support development of the solar PV and generally RES energy sector in Serbia as a country with great potential for utilizing PVs. The results of present study show that there is a lot of administrative work to be done (policy-making, educational support and RES and PVs promotion) in order to achieve expected results from solar PV power engineering in the future.

Radosavljevic J.,University of Pristina in Kosovska Mitrovica
Applied Artificial Intelligence | Year: 2016

This article presents a new hybrid algorithm based on particle swarm optimization (PSO) and the gravitational search algorithm (GSA) for solving the combined economic and emission dispatch (CEED) problem in power systems. Performance of this approach for the CEED problem is studied and evaluated on three test systems with 3, 6, and 40 generating units, with various cost curve nature and different constraints. The results obtained are compared to those reported in the recent literature. Those results show that the proposed algorithm provides an effective and robust high-quality solution of the CEED problem. © 2016 Taylor & Francis.

Petkovic D.,University of Niš | Shamshirband S.,University of Malaya | Kamsin A.,University of Malaya | Lee M.,Chonbuk National University | And 2 more authors.
Renewable and Sustainable Energy Reviews | Year: 2016

The main objective of wind farm modeling is to maximize wind farm efficiency. The optimal wind turbine placement on a wind farm could be modified by taking economic aspects into account. The net present value (NPV) is the most important criteria for project investment estimating. The general approach in deciding the distinctive choice for a task through NPV is to treat the money streams as known with conviction. Even little deviations from the decided beforehand values might effectively negate the choice. To assess the investment risk of wind power project, this paper constructed a process that selected the most influential wind farm parameters on the NPV with adaptive neuro-fuzzy (ANFIS) method. This procedure is typically called variable selection, which corresponds to finding a subset of the full set of recorded variables that exhibits good predictive abilities. Variable seeking utilizing the ANFIS system was performed to figure out how the seven wind farm parameters affect the NPV of the wind farm. © 2015 Elsevier Ltd. All rights reserved.

Radosavljevic J.,University of Pristina in Kosovska Mitrovica | Jevtic M.,University of Pristina in Kosovska Mitrovica
Elektronika ir Elektrotechnika | Year: 2016

The optimal reactive power dispatch (ORPD) is achieved by optimal coordination of the equipment which control the reactive power flows in the power system. The (ORPD) can be mathematically formulated as a nonlinear, static and large-scale optimization problem with constraints. This paper deals with solving the ORPD problem using a new hybrid algorithm consisting of gravitational search algorithm (GSA) and sequential quadratic programming (SQP). The performance of this hybrid algorithm for the ORPD problem is studied and evaluated on the standard IEEE 30-bus test system with two different objective functions, namely minimization of real power loss and voltage profile improvement. © 2016, Kauno Technologijos Universitetas. All rights reserved.

Anicic O.,University of Pristina in Kosovska Mitrovica | Petkovic D.,University of Niš | Cvetkovic S.,University of Pristina in Kosovska Mitrovica
Renewable and Sustainable Energy Reviews | Year: 2016

Noise annoyance caused by wind turbines has become a great problem in recent years, due to the rapid increase in number of wind turbines, triggered by sustainable energy goals set forward at the national and international level. Up to now, not all aspects of the generation, propagation and perception of wind turbine noise are well understood. For a modern large wind turbine, aerodynamic noise from the blades is generally considered to be the dominant noise source, provided that mechanical noise is adequately eliminated. The sources of aerodynamic noise can be divided into tonal noise, inflow turbulence noise, and airfoil self-noise. Many analytical and experimental acoustical studies performed the wind turbines. Since the wind turbine noise level analyzing by numerical methods could be very challenging and time consuming, soft computing techniques are preferred. The objective of this article was to estimate noise level of wind turbine by support vector regression (SVR) procedure. To build an effective wind turbine noise level prediction model, the polynomial and radial basis function (RBF) are applied as the kernel function of SVR in this research study. According to the results, a greater improvement in estimation accuracy can be achieved through the SVR with radial basis function compared to SVR with polynomial basis function. © 2015 Elsevier Ltd. All rights reserved.

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