Papers by Keyword: Fractal

Abstract: The conducted research program was focused on the creation steel fiber reinforced concrete (SFRC) dedicated for casting columns with fractal based cross-sections. The columns in question were planned to be cast using 3D printed plastic formworks. Harnessing 3D printing of plastic enables easy creation of cross-sections which are not possible to be achieved using traditional formwork techniques. The mix had to be characterized by consistency enabling almost self-compacting behavior, reasonably high volume of fiber (volumes of fiber ranging from 0.5% to 2.0% were considered) and the maximum diameter of used aggregate of 2mm. Due to very complicated cross-sections of planned columns the mix had to be able to effortlessly penetrate very elaborate shapes of fractal formwork. All desired properties were achieved during the research program using two admixtures and micro steel fiber. The mix was tested using column specimens with circular, square and pentagon cross-sections.

Abstract: A hexagonal shaped repeated loop structure with reconfigurable ground stub technique is proposed for ultra-wideband (UWB) application. Effects of repeated loops in the fractal structure and position of reconfigurable ground stub are optimized for ultra-wideband characteristics with better performance of the antenna. Two PIN diodes are used in the ground stub to achieve reconfigurability. The proposed fractal antenna is designed with FR4 substrate with an overall dimension of 40×44×1.6 mm³. The design shows frequency reconfiguration from Ultra-wideband characteristics to multiband for different possible switching conditions. The entire design is carried out in CST 2018 environment and the simulated results show that the proposed design is suitable for sub 6GHz wireless LAN, Bluetooth, WiMAX and other wireless applications.

Abstract: The characteristics of the macrostructure of expanded clay concretes are compared using the topological and fractal approaches. The sensitivity of concrete strength to the fractal dimensions of a cement-sand matrix, expanded clay gravel, feldspar grains, large fractions of quartz and pores is verified. The trend of the influence of the expanded clay concrete macrostructure on its strength is determined using the fractal approach. Fractal modeling of the macrostructure of expanded clay concrete made it possible to reduce the forecast error in the indices of their strength by 1.18...2.03 times in comparison with the topological approach.

Abstract: The self-organization of COOH-functionalized multiwall carbon nanotubes (MWCNTs) during droplet evaporation of their aqueous suspension in a constant uniform electric field (E) was investigated. It was established that the COOH-functionalization polarizes the MWCNTs in the transverse direction to their axis. Depending on their size, MWCNTs tended to agglomerate into three different stable structures in different drop regions. There were linear, fractal and cluster structures (LS, FS, and CS). Sizes of the FSs decreased as 1/Е, whereas the rate of their growth increased as Е². The single-walled carbon nanotubes (SWCNTs) were found inside the LSs and CSs. The chiral indices of the SWCNTs were determined, corresponding to metallic and semiconducting conductivities. An analysis showed that as a result of coagulation and amassment of the carbon nanotubes (CNTs) near electrodes, there were formed conductive regions. When the concentration of MWCNTs reached some value in part nearest to an electrode, this part became conductive. The positive and negative electrodes, formed now by MWCNTs, shifted towards each other. The observed effects show that considered self-organization is controllable by the electric field.

Abstract: Nondestructive penetrant testing is effective, and in some cases, it is the only possible method of accidents prevention at high-risk sites. But in nowadays liquid-filled discontinuity model has not been adequately studied. Hydrodynamics in the open-end capillaries characterize the flow of liquids using the methods of leak detection. To detect surface discontinuities that are capillary, capillary flaw detection methods are used. Until now, the theoretical relation l = l (t) has not been find out. This relation makes it possible to calculate the absorption kinetics in any capillary at all its stages, which would coincide with experimental data with high accuracy. The studies show that the time of filling the capillaries by liquid is usually higher than the theoretically predicted one. Therefore, revealing the regularities of filling capillaries with liquids to the maximum depth and the duration of filling the capillary with liquid by a given depth is an actual task. The authors suggest a model for determining the velocity of fluid in dead-end and open-end and through capillaries, which take into account the fractal topology of the surface.

Abstract: We have studied the effect of tin microalloying on the kinetics of the fractal mesodefect structure of melt-spun Fe₇₀Cr₁₅B₁₅(Sn) alloys during thermal loading. It is established that the morphology evolution of ribbon interfaces correlates with the kinetics of physical properties. Symmetry character of melt-spun alloys is identified by the form of fractal dimensionality spectrum. Reduction of the fractal dimension is observed at stages of both vitrification and nanocrystallization. Residual alloying by tin of the contact interface of ribbon changes a topology of the localized states that lowers the temperature of vitrification.

Abstract: The scanning process of fused deposition modeling is realizing the fill of certain region, Therefore, reasonable scanning path planning directly affects the forming efficiency and the precision of the work piece. The method of Hilbert curve fractal scanning path which basing on the characteristics of both partition and parallel scanning is put forward basing on the analysis of the existing scanning mode. Application of improved curve filling method for complex curved surface forming planning, according to the characteristics of the Hilbert curve and Hamilton circuit, combined with the characteristics of the scanned level scan path trajectory planning, generate a continuous and comprehensive function value which the weight minimum scanning track under the premise of ensuring the quality of scanning. In order to avoid the generation of island type trajectory, setting a decimal for each loop can easily distinguish between each circuit, finally obtains the scan trajectory. The method can be used to generate scanning track continuous greatly reducing the spray head start and stop times and improves the processing efficiency of the whole, not only to meet the accuracy requirements and can generate non scanning path interference but also high forming efficiency.

Abstract: This paper presents tool for analysis of CFD adapted for flows in multi-staged stirred vessels with fractal pattern baffled for industrial. In order to develop a good mixing process model for stirred tanks, several way have been investigated by using the computational fluid dynamic. Implementing fractal design into stirred tank’s baffle and impeller are believed to influence the flow characteristic inside the stirred tank. The mixing process will be conduct by using multi-stage stirred tanks. Hence, the study is to simulate a fractal pattern baffled stirred vessels with fractal base of impeller. Four models with a new concept and different design of stirred tank have been introduced and studied. The multi-stages stirred tanks will adapted with fractal base pattern concept. The simulation is carry out by using the standard k-ε turbulence model. The results have been analysis in order to prove that which one of that model is the most effective in mixing. The flows produced in stirred tank are different and relevant with each model. The velocity profiles also give a relevant and quite impressive result by each model. At the end, the results will be examined and compared with each data that use a common type of baffle and impeller design.

Abstract: This paper described the use of inkjet printing to design multiband fractal antenna based on Sierpinski arrowhead curve architecture. The antenna is printed using silver nanoparticles on a plastic substrate PET (Polyethylene terephthalate). Using a combination of printing technology and fractal geometry to achieve very advanced parameters in three frequency bands 650 MHz, 1,57 GHz and 2,5 GHz. Multiband antenna may find application in specific portable devices, where it would be possible to implement the antenna housing facilities in the form of printing.

Abstract: Palm oil and methanol do not form a single phase mixture in transesterification process in stirred tank due to a poor surface contact between them; hence give a relatively slow mixing process of the mixing. Introduction of new baffles in the stirred tank with a fractal pattern due to the fractal shape can give a high turbulent level when a fluid flow through the fractal pattern is the new idea in optimizing the using of the fractal pattern in engineering especially in mixing industries. Hence, in the present study, a new concept of baffles with a fractal design was proposed to enhance a palm oil-methanol mixing in stirred tank. In order to achieve the objective, the simulation of palm oil-methanol mixing was carried out by using ANSYS Fluent software. The simulation was carrying out primarily in the stirred tank equipped with the fractal baffles and the levels of mixing were observed at 60, 120, 180 and 240 seconds after the beginning of introduction of methanol in the stirred tank. An effectiveness of the fractal baffles will be evaluated by determining the Coefficient of Variation (COV). The simulation results also were compared in term of homogeneity level of palm oil-methanol mixing to the normal baffles in order to determine the significant effect of the fractal baffles. Based on the simulation results, the value of COV for the mixing process in the stirred tank equipped with fractal baffles at the selected time interval are 0.066, 0.0436, 0.0326 and 0.0226 respectively. Since the values of COV between 0.01 and 0.05 are a reasonable target for many industry applications, the results for new approach of stirred tank with fractal baffles represent completely homogeneous mixing for the palm oil-methanol simulated in this study. Definitely this new approach of fractal baffles gave better results because of lower number of COV compared to the stirred tank with normal baffles.