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Arşivlenen Tez
Behavior of geopolymer concrete under impact
This study investigates the properties of self-compacted geopolymer concrete (SCGC) obtained by ground granulated blast furnace slag (GGBFS) as binder in both the fresh and hardened states under the combined addiction of nano-silica (NS), steel fibers (SFs) and recycled tyre rubbers (RTR). While eighteen different mixtures were used in the experimental study, a total of thirty-six beam specimens were produced for the study. Those eighteen mixtures of SCGC contained different percentages of NS (0% and 2%) and different percentages of SFs (0%, 0.5% and 1%) and different percentages of RTR (0%, 10% and 15%). 100% GGBFS with a fixed alkaline activator-to-binder ratio of 0.5 was used as a binder to prepare the SCGC mixes. A blend of sodium-silicate (Na2SiO3) solution and sodium hydroxide (NaOH) solutions with a ratio of 2.5 has been chosen as an alkaline activator. The fresh and hardened states concrete tests including slump, flow ability, workability and compressive, impact and flexural strengths were realized in the study. Experimental results were examined in detail to determine the influence of important factors on mechanical performance of SCGC. Furthermore, correlations among the empirical data were evaluated to explore the relations between the hardened and fresh states properties of SCGC. Experimental results showed that the combined use of NS and SFs affected the fresh state properties adversely, while it improved the impact and flexural properties of the SCGC samples considerably. Moreover, the influence of NS was predominant regarding the fresh state performance and compressive strength, while the effect of SFs were superior regarding flexural and impact strength. Moreover, incorporating of RTR influenced the fresh state properties reversely, while the effect of SFs with RTR was superior regarding flexural and impact strength.
Improvement of signal significance of Ds± meson's signalvia using artificial neural network
The aim of the analysis is to improve the significance of the Ds ± meson signal in ALEPH data which is recorded at LEP in the Ds± → π± + φ where φ mesons are reconstructed from φ →K+ K- decay channel. The analysis covers two phases. In first phase, reconstruction of particles in the decay channel is performed and input variables are stored to be used in classification. This phase is the machine learning part of the analysis. The second phase is the selection of an optimum algorithm for classification of signal and background. Improvement of significance of Ds meson's signal is performed after selection of the optimum algorithm and the evaluation of coefficients for relevant input variables which are stored in first phase. Classification is performed with the Toolkit for Multivariate Analysis (TMVA) which operates under the ROOT data analysis framework. TMVA includes many classification algorithms; the Boosted Decision Tree method is chosen as the optimum classification method.
Modular multilevel converter design
Modular multilevel converter (MMC) has many submodules in each phase. Hence, it has many operating advantages such as modularity, flexibility, ability to generate high voltage and low harmonic content at the output. Selecting the arm inductance to obtain satisfactory MMC performance is one of the critical design constraints of the MMC. Since it affects the fault/circulating current magnitudes, efficiency as well as the harmonic content at the output. In this thesis, a novel procedure has been conducted to find the optimum value of the arm inductor when considering the factors of DC voltage utilization, harmonics and efficiency of the MMC. On the other hand, capacitor voltage balancing is an important issue in MMC operation. Unequal SM capacitor voltages cause improper operation of the MMC, resulting in high circulating currents, reduced efficiency and low harmonic quality at the output. Carrier swapping method can overcome the voltage balancing problem without any need for voltage and current sensors. In this thesis, a swapping method has also been proposed suitable for applying to different switching modulation schemes for MMC. More specifically, this swapping method has been used for the first time for Nearest Level Modulation (NLM) scheme in the literature. The optimum swapping frequency for each modulation scheme has been determined by performing case studies on the MMC. For all studies, the models are first developed in the simulation environment for verification and finally, the experimental studies are conducted to validate the results.
Biochemical responses of oncorhynchus mykiss to the stress induced by phosmet
Organophosphorus pesticide phosmet is an anticholinesterase showing its toxicity following contact, ingestion and inhalation. It finds a use in agriculture for apple, peach and olive trees against pests in our country and there are limited numbers of study related to its sublethal effects of on non-target organisms. Therefore this investigation was performed to evaluate oxidative stress inducing potential and anticholinesterase activity of phosmet together with biochemical blood parameters on liver and brain tissues of juvenile O. mykiss following 24h, 48h, 72h and 96h of exposure to 5 µg/L, 25 µg/L and 50 µg/L concentrations. Phosmet application resulted in important decrease in the levels of serum glucose, protein and cholesterol while a significant increase in the activities of ALT, AST and ALP were recorded. Its anticholinesterase activity was confirmed in both liver and brain tissues being more pronounced in brain possibly due to abundant tissue concentration. In both tissues, the activities of SOD, CAT and GPx and level of GSH were increased. Similarly, TBARS level exerted ascending tendency. Obtained findings reveal the inhibitory effect of phosmet on AChE activity and its oxidative stress potency. The observed changes in ALT, AST and ALP activities present the hepatotoxic potential of phosmet meanwhile determined hypoproteinemia and hypoglycaemia were evaluated as adaptive responses to cope with the applied stress.
Heat transfer enhancement in a tube by variable cross section twisted tape
In this thesis, a numerical study is conducted to investigate the influence of spherical-shaped and teardrop-shaped patterned walls of twisted tapes on thermo-hydraulic performance enhancement. All patterned twisted tapes were investigated by using Ansys Fluent under a constant heat flux of 5 W/cm2 for Reynolds numbers (Re) within the range of 3000 – 27000. Besides, they have different pattern numbers (0, 30, and 45) and three different kinds of arrangement (composed of only dimples, only protrusions, and a combination of dimples and protrusions) with a constant twist ratio of 3. Furthermore, the configurations of teardrop patterned twisted tapes align in two different flow directions. The results show that the dense spherical dimpled-protruded twisted tape (D-DPT) and the dense teardrop dimpled-protruded twisted tape (D-TDP) reach the highest thermal performance factor (TPF) values of 1.508 and 1.517, respectively at Re=3000. All patterned twisted tapes have higher Nusselt number (Nu) values than traditional twisted tape (TT) in the tested Re region. Moreover, all dense versions of them have higher Nu and friction factor (f) than those of their sparse versions.
Development of multi-level inverter for power quality enhancement
The objective of this thesis is to develop and improve the performance of the multi-level inverter. Two paths have been followed in the development and improvement works. The first one represents the off grid connected multi-level inverter. The trend is focused to increase the number of the level at the output of the inverter while the inverter represents the main energy source. In the second path followed in the studies, the grid-connected multi-level inverter has been considered. Power quality enhancement has been done by developing the control unit of grid connected multi-level inverter in such a way to ensure the stability of the system against the system voltage sag. The multilevel inverters designed in the thesis are both simulated using a computer software program and implemented in hardware. The developed inverters are multilevel and hybrid inverters. Conventional inverters give five levels in the output waveform. These inverters contain two H-bridge circuits to generate different levels at the output while the hybrid inverter developed in the thesis includes three H-bridge circuits to form different levels at the output. Moreover, developed hybrid inverter can also operate in conventional mode when it is supplied with equal sources. The output of each H-bridge has been connected in a cascaded form. The sum of the individual H bridges voltages represents the final inverter voltage. Experimental results on the developed circuits gave satisfactory results and confirmed the accuracy of the design. Key Words: Low Voltage Ride Through (LVRT), Photovoltaic Panel (PV),Multi Level Inverter, Maximum Power Point Tracking (MPPT), Active And Reactive Power Control
Post-fire behavior of composite column-column connections
The Columns made of Concrete-Filled Steel Tubes (CFST) Connections have proved to be a cost-effective method of composite construction because they enable structures to be dismantled during their service life. Although the behavior of CFST column connections under many different loading scenarios has been well detailed, the postfire resistance of CFST column connections is not proposed in the literature yet. This study shows the possibility to use CFST columns with a bolted-flange connection to advance their post-fire resistance. To this end, CFST columns with and without stiffeners were subjected to standard fire exposure. To address their post-fire performance. The samples are classified into two groups: group 1, stiffener-free connection, and group 2, in which stiffeners are included. Three thicknesses of the bolted-flange were used such as 2, 4, and 6 mm. The results indicated that the different thicknesses of bolted-flanges in group 1 samples the axial stiffness value had some effect and in group 2 samples this effect had been doubled. The stiffeners played a significant role in the toughness value and it was reduced with the reducing of stiffeners thickness. Also, the ductility improvement was notable in stiffened samples. Accordingly, it can understand that the bolted-flange connection of the CFST column have a significant role in fire resistance without adding any external protection materials.
High bit rate indoor visible light communication (vlc) system
In general, visible light communication (VLC) systems run at low data rates. By introducing multiple input and multiple output (MIMO) techniques, services at enhanced data rates can be viable for VLC systems. This work proposes MIMO technique to attain VLC system with high data rates. To attain MIMO method this system includes a number of photodiodes with a narrow field of view (FOV), which highlights the benefit of using MIMO technology in improving the data rate. The results show that using MIMO technique leads to enhance the VLC system when it is compared with the traditional system (without using MIMO). The results show that an improvement in the signal-to-noise ratio (SNR) level, which is the most attempt to determine communication quality, increasing the channel bandwidth and reducing the delay spread are achieved when MIMO technique is used. The proposed system focuses on transferring data in parallel, which adds a significant improvement in the aggregate data rate compared to the traditional VLC system. The results show that the maximum aggregate data rate is 3.4 Gbps in the 4 x 4 MIMO-VLC system while it reaches 6.8 Gbps on the 8 x 8 MIMO-VLC system. The improvement in SNR level in the two proposed systems greatly improves the aggregate data rate.
Reflector savings in calculation of the critical mass
The critical mass which is known as the smallest amount of fissile material required in any system of geometry for a sustainable fission chain reaction can be approximately calculated by using the steady-state one-group neutron diffusion equation. In the solution of the diffusion equation, it is important if the core is just bare or surrounded by a reflector material. In such analytical calculations, it is seen that the mass and size of the bare system decreases dramatically if there is reflector material. This thesis considers the application of Monte Carlo Method to hypothetical bare and reflected systems in spherical, cylindrical and rectangular coordinates, and compares its results with those of analytical solutions of neutron diffusion equation for bare and reflected systems in three basic geometries, respectively. We show that our numerical calculations for the size of the systems in these geometries by Monte Carlo Method are in very good agreement with those of the analytical solutions. Our method is very simple, understandable and applicable in any computer program language, and the results are in consistent with those of analytical ones.
Natanson tipi integral eşitsizlikleri üzerine
Bu tez çalışması üç bölümden oluşmaktadır. Tezin birinci ve ikinci bölümlerinde diğer bölümlerde kullanılacak bazı tanım ve teoremlerle birlikte açıklayıcı ve kullanışlı örnekler verilmiştir. Üçüncü bölümde ise bazı Natanson tipi integral eşitsizliklerinin ispatı verilmiştir. Natanson tarafından verilen lemma integrallenebilir bir fonksiyonun karakteristik noktalardaki temsil problemine bir cevap olarak çeşitli yazarlar tarafından genelleştirilmiş ve tekil integral teorisindeki uygulamalarda kullanılmıştır. Bu eşitsizliğin bazı genellemeleri Mamedov, Taberski ve Gadjiev tarafından literatüre kazandırılmıştır. Verilen bu genellemeler tekil integraller teorisinin uygulamaları olarak sunulmaktadır. Bu tez çalışmasında I.P. Natanson'dan S. Siudut' a Natanson Lemma'da verilen integral eşitsizliğinin çeşitli genellemeleri incelenmiş ve derlenmiştir.