Hamzaçebi C.

Article | 2008 | Applied Mathematics and Computation196 ( 1 ) , pp.309 - 317

The genetic algorithms (GAs) can be used as a global optimization tool for continuous and discrete functions problems. However, a simple GA may suffer from slow convergence, and instability of results. GAs' problem solution power can be increased by local searching. In this study a new local random search algorithm based on GAs is suggested in order to reach a quick and closer result to the optimum solution. © 2007 Elsevier Inc. All rights reserved.

Tutkun N.

Article | 2009 | Expert Systems with Applications36 ( 4 ) , pp.8172 - 8177

In this study, a new crossover approach to the real-coded genetic algorithm is proposed. The approach is simply based on efficiently tuned real-coded crossover operation using the probability distribution function of Gauss distribution to generate rather dissimilar strings which may be candidates of possible solutions. Also linear and quadratic mapping algorithms comparatively used both to constrain individuals in the given search spaces and to produce different individuals in order to increase average fitness relatively for the same population. Moreover, to refine genetically found optimum points the local search technique based on . . . Newton's method was performed. The designed software was first implemented on 11 well-known test functions and their results were compared with previous findings as shown in tables. In few test functions, the elitism operator was put into effect to maintain fitness stability helping increase the search performance of the proposed algorithm. The results indicate that the solutions to the test functions were almost the same with theoretical ones and the number of function evaluations for each test function was less than that obtained from using previous approaches. © 2008 Elsevier Ltd. All rights reserved Daha fazlası Daha az

Tutkun N.

Article | 2008 | Renewable Energy and Power Quality Journal1 ( 6 ) , pp.335 - 338

The pulse width modulated power inverters have been increasingly using to convert DC power to AC power in small wind plants. When these inverters are used for power conversion, the integrated output voltage waveform is inevitably distorted. Although increasing the switching frequency is one choice to achieve the smoother output voltage, it adds extra harmonics to the output. There are various techniques such as analogue filtering, harmonic elimination etc. to reduce the number of harmonics usually affecting the system performance. In this study, a simple but efficient modulation approach based on the optimization of the shape of the . . . triangular voltage waveform is proposed. The results have shown that the total harmonic distortion of the optimized voltage waveform decreases gradually and thus helps improve on the power quality during the conversion. © 2008, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved Daha fazlası Daha az

Tutkun N.

Article | 2010 | Expert Systems with Applications37 ( 8 ) , pp.5614 - 5620

Inverters are such electronic devices that are extensively used to convert DC power to AC power in wide-range domestic and industrial applications. DC power is usually supplied from either national grid through the rectifiers or batteries for high and low energy demands, respectively. When they are employed to feed electrical devices the efficiency of these devices tends to decrease due to harmonic occurrence in them. One solution to this problem is the selective harmonic elimination which is required to solve multiple non-linear equations simultaneously. These equations are mainly function of the switching angles and are obtained f . . .rom a type of inverter output voltage such as being unipolar, bipolar, etc. To eliminate one or more harmonics in these output voltages becomes a typical multivariate root-finding problem and its solution requires root-finding methods such as the Newton-Raphson method, the Broyden method etc. These methods can only produce a meaningful solution if initial values are properly guessed, but it is highly difficult task due to having no direct formula. In this paper, the hybrid genetic algorithm method based on the refinement of the genetic algorithms results through the Newton-Raphson method was used to simultaneously solve the non-linear equations. The results have shown a considerable effect on decrease in the total harmonic distortion, thereby increasing the efficiency of devices compared to conventional methods under the same conditions. © 2010 Elsevier Ltd. All rights reserved Daha fazlası Daha az

Tutkun N.

Article | 2006 | Journal of Magnetism and Magnetic Materials300 ( 2 ) , pp.506 - 518

Recently estimation of iron losses in electrical steels have become very significant for the manufacture of well-designed magnetic devices that are to be subjected to electronically generated voltage excitations such as pulse width-modulated (PWM) voltage excitation. In this study, iron loss components were estimated by means of the genetic algorithms method and electrical steel manufacturers' data. The results were compared with those obtained by a widely used classical method. The comparison has shown that the genetic algorithms method improved loss estimation with respect to the classical method under both sinusoidal and PWM flux . . . conditions. © 2005 Elsevier B.V. All rights reserved Daha fazlası Daha az

Tutkun N. | Moses A.J.

Article | 2004 | Journal of Magnetism and Magnetic Materials284 ( 01.Mar ) , pp.201 - 205

Toroids wound from grain-oriented 3% Si-Fe have been widely used for building various types of electromagnetic devices. Although magnetic properties of a typical toroidal core are provided in data sheets, its approximate equivalent parameters are not frequently given. When such devices are used in manufacturing process, their simplified equivalent circuit parameters are required without interruption of production line in case of a system failure. This investigation makes an attempt to estimate these parameters using a simple genetic algorithm method. The obtained results are slightly different from the measured results under sinusoi . . .dal excitation at flux densities varied from 1.3 to 1.7 T, 50 Hz. © 2004 Elsevier B.V. All rights reserved Daha fazlası Daha az

Kömürcü M.I. | Tutkun N. | Özölçer I.H. | Akpinar A.

Article | 2008 | Applied Mathematics and Computation195 ( 1 ) , pp.49 - 60

Waves, topographic characteristics and material properties are the most significant factors, which affect the sediment movement and coastal profiles. In this study, considering the wave height (H0) and period (T), the bed slope (m) and the sediment diameter (d50), the cross-shore sediment movement is investigated using a physical model and obtained 80 experimental data for offshore bar geometric parameters. The experimental results are also evaluated by the genetic algorithms (GAs) that are limitedly employed in coastal engineering applications. The results of GAs model and equations cited in the literature are compared with the exp . . .erimental results. It is concluded that estimates of bar parameters by the GAs give a better estimation performance with respect to other conventional methods. © 2007 Elsevier Inc. All rights reserved Daha fazlası Daha az