Vojislav V. Mitić

Wind speed parameters sensitivity analysis based on fractals and neuro-fuzzy selection technique

Fluctuation of wind speed affects wind energy systems since the potential wind power is proportional the cube of wind speed. Hence precise prediction of wind speed is very important to improve the performances of the systems. Due to unstable behavior of the wind speed above different terrains, in this study fractal characteristics of the wind speed series were analyzed. According to the self-similarity characteristic and the scale invariance, the fractal extrapolate interpolation prediction can be performed by extending the fractal characteristic from internal interval to external interval. Afterward neuro-fuzzy technique was applied to the fractal data because of high nonlinearity of the data. The neuro-fuzzy approach was used to detect the most important variables which affect the wind speed according to the fractal dimensions. The main goal was to investigate the influence of terrain roughness length and different heights of the wind speed on the wind speed prediction.

Fractal Geometry and Properties of Doped BaTiO3 Ceramics

Taking into account that the complex grain structure is difficult to describe by using traditional analytical methods, in this study, in order to establish ceramic grain shapes of sintered BaTiO3, new approach on correlation between microstructure and properties of doped BaTiO3 ceramics based on fractal geometry has been developed. BaTiO3 ceramics doped with various dopants (MnCO3, Er2O3, Yb2O3) were prepared using conventional solid state procedure, and were sintered at 1350oC for four hours. The microstructure of sintered specimens was investigated by SEM-5300. Using method of fractal modeling a reconstruction of microstructure configurations, like grains shapes, or intergranular contacts has been successfully done. Furthermore, the area of grains surface was calculated using fractal correction that expresses the irregularity of grains surface through fractal dimension. The presented results, indicate that fractal method for ceramics structure analysis provides a new approach for describing, predicting and modeling the grain shape and relations between the BaTiO3-ceramic structure and dielectrical properties.

MICROSTRUCTURE CHARACTERIZATION OF POROUS MICROALLOYED ALUMINIUM-SILICATE CERAMICS

Kaolinite and bentonite clay powders mixed with active additives, based on Mg(NO 3 ) 2 and Al(NO 3 ) 2 , sintered at high temperatures produce very porous ceramics with microcrystalline and amorphous regions and highly developed metalized surfaces (mainly with magnesium surplus). Microstructure investigations have revealed non-uniform and highly porous structure with broad distribution of grain size, specifically shaped grains and high degree of agglomeration. The ceramics samples were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction analysis (XRD) and IR spectroscopy analysis, prior and after treatment in “synthetic water”, i.e. in aqueous solution of arsenic-salt. Grain size distribution for untreated and treated samples was done with software SemAfore 4. It has shown great variety in size distribution of grains from clay powders to sintered samples.

TRIZ Creativity Approach to the Design of an Innovative Wind Turbine System

The main aim of a conceptual design is to obtain the innovative projects or ideas to enable the products and designs with best performance, what is also including the materials especially ceramics optimal selection for the effective solutions. The theory of inventive problem solution (TRIZ) is a systematic methodology for innovation. The design of a wind turbine system as an engineering example is illuminated in this paper to show the significance and approaches of applying TRIZ in getting the creative conceptual design ideas. In recent years the use of renewable energy including wind energy has risen dramatically. Because of the increasing development of wind power production, improvement of the design and control of wind turbines is necessary. To optimize the power produced in a wind turbine, it is important to analyze the wind turbine designs and systems. To build a wind turbine model with the best features, it is desirable to analyze factors that are truly relevant to the converted wind energy. The main aim of this work is to show a systematic methodology for innovation as an effective procedure to enhance the capability of developing innovative products and to overcome the main design problems. The TRIZ method will be used in order to eliminate the technical contradictions which appear in the wind turbine systems.

Processing parameter influence on BaTiO3 ceramic fractal microstructure and dielectric characteristics

Abstract In the process of BaTiO3 ceramics consolidation, technological parameters like sintering temperature, pressing pressure and additives significantly determine the microstructure and electrical properties. Slight change of a particular sintering parameter can considerably change the microstructure as well as the electrical parameters. Structural complex grain–contact–grain is observed on Ho doped BaTiO3 ceramics, sintered from 1320 to 1380°C. The new configuration model of ceramic grain contact surfaces is presented in this paper. This model is based on Coble’s two-sphere approximation and its generalisation to ellipsoidal geometry. The integral contact surface directly influences the value of the total ceramic capacity. Fractal method is applied for intergrain contact analysis. Ceramic grains are considered to have fractal surface (as it is elsewhere in nature) and, therefore, fractal structure influences on the dielectric properties of BaTiO3 ceramics. The obtained results give better understanding of ceramic microstructure with the final aim to establish significant interrelation among processing, structural and electrical parameters.

Fractals and BaTiO3-Ceramic Microstructure Analysis

The complex grainy structure of BaTiO3 is difficult to describe by using traditional analytical or geometrical methods. Here, an attempt is made to establish new mathematical models based on both Euclidean and fractal geometrical methods. The first uses ellipsoidal approximations for barium-titanate grains describing the contact area as surface patches with an ellipsoidal boundary. The fractal method offers a better approach in describing the irregular and wavy surface of such contact zones and therefore, it defines aspects that are complementary to those defined by Euclidean methods. Electric, ferroelectric and opto-electric properties of BaTi03 are influenced strongly by the fractal dimension of the intergranular contact surfaces. This parameter is measured in a laboratory environment using SEM micrographs with different magnifications. The BaTiO3 samples examined have been sintered using different sintering pressures and temperatures. Then, the fractal dimension is calculated from a log-log diagram, and the grain contours are constructed using Iterated Function Systems connected with fractal interpolation.

Microstructure and Dielectric Properties of Rare-Earth Doped BaTiO3 Ceramics

The specimens of BaTiO3 doped with 0.01, 0.1 and 0.5 wt% of Er2O3 or Ho2O3 used for this investigation were prepared by the conventional solid state reaction. The specimens were sintered at 1350°C in an air atmosphere for 4 hours. The grain size and microstructure characteristics for various samples and their phase composition was carried out using a scanning electron microscope SEM equipped with EDS system. SEM analysis of Er/BaTiO3 and Ho/BaTiO3 doped ceramics showed that in samples doped with a low level of rare-earth ions, the grain size ranged from 10–60μm, while with the higher dopant concentration the abnormal grain growth is inhibited and the grain size ranged between 2–10μm. We also applied the fractal method in microstructure analysis of sintered ceramics especially as influence on dielectric properties of BaTiO3 ceramics. These fractal effects have been used for better understanding of intergranular capacitors.

Adaptive Neuro-Fuzzy Optimization of Wind Farm Project Investment Under Wake Effect

The engineering planning of a wind farm generally includes critical decision-making, regarding the layout of the turbines in the wind farm, the number of wind turbines to be installed and the types of wind turbines to be installed. Two primary objectives of optimal wind farm planning are to minimize the cost of energy and to maximize the net energy production or 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) and internal rate of return (IRR) are two of the most important criteria for project investment estimating. To assess the investment risk of wind power project, this paper constructed a process which initially simulated maximal NPV with adaptive neuro-fuzzy (ANFIS) method and then evaluated the IRR based on it. Afterwards, ANFIS simulated maximal IRR and then evaluated the NPV based on it. ANFIS shows very good learning and prediction capabilities, which makes it an efficient tool to deal with encountered uncertainties in any system. The aim of this paper is to develop a model to determine economically optimal layouts for wind farms which include the aerodynamic interactions between the turbines, the various cost factors and wind regime.

BaTiO3-ceramics electrical model based on intergranular contacts

Abstract This paper presents the contribution to the development of methods for electronic parameters recognition in BaTiO 3 -ceramics grains contacts. The model of intergranular impedance applied on two-grain contact is considered and it is established using the equivalent electrical scheme characterized by corresponding frequency characteristic. Globally, BaTiO 3 -ceramics sample is consisted of a huge number of mutually contacted grains which form clusters. For each of them, it is possible to establish the equivalent electrical model and for defined set of input parameters using symbolic analysis to obtain the frequency diagram. The support for the idea of establishing the electrical model based on intergranular contacts is founded in the fact that results obtained for the equivalent impedance of the cluster (for more then three grains) by symbolic simulation are similar to results measured on real BaTiO 3 -ceramics samples, which confirmed the validity of approach.

Modeling of intergranular impedance as a function of consolidation parameters

In this paper, the time-temperature dependent intergranular impedance model is defined on the basis of intergranular capacitance model and grain growth model. The relations between the most dominant electrical parameters (capacitance and conductance) of the intergranular microcondenser, and geometric parameters are established.