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Evrilen akıllı sistem ile attas uçağının aerodinamik özelliklerinin yakalanması
No full textThesis (M.Sc.) -- Istanbul Technical University, Graduate School, 2025There are many studies in the literature that have been conducted to obtain an accurate mathematical model. In the early times, modeling studies were done with differential equations, but this approach could not fully express the nonlinear characteristics in some cases. Later, it was seen that nonlinear systems can be modeled successfully with the development of artificial intelligence and fuzzy systems. Especially in the aviation industry, where safety and security are of paramount importance, it is critical to accurately represent aircraft models. Mathematical models that accurately represent aircraft dynamics are critical in many studies such as aircraft control system design development, certification, and flight mechanics analysis. Therefore, aerodynamic modeling of the aircraft is very important. Either a wind tunnel or a parameter estimation method is used for aerodynamic modeling. However, wind tunnel, which is an experimental method, is quite costly since it requires an experimental setup. For this reason, many statistical-based system identification algorithms have been developed in the literature to estimate aerodynamic control and stability derivatives using measured flight tests. The Ordinary Least Squares (OLS) method is the most widely used system identification algorithm. In this method, which belongs to the light gray box model category, an aerodynamic mathematical model is developed that best fits the flight dataset and minimizes the squares of the differences between the estimated value and the actual value. However, this method may not be fully successful in expressing the nonlinear characteristics of the aircraft. In the neural network (NN) algorithm, which is in the black box model category, the weight parameters are trained using the input data and output data of the aerodynamic postulated model. The model obtained as a result of the NN algorithm can successfully represent the nonlinear characteristics of the aircraft. However, it is not possible to interpret NN based model since they lack a rule base in their structure. On the other hand, the models obtained with fuzzy logic algorithms are open to interpretation because they have a rule base structure and these models are in the dark gray box model category. Moreover, fuzzy logic algorithms are very successful in modeling complex and nonlinear systems. Considering these advantages of fuzzy systems, many aerodynamic modeling studies have been conducted in the literature with Adaptive Network Based Fuzzy Inference System (ANFIS). Based on these observations, Evolving Type 1 Quantum Fuzzy Neural Network (eT1QFNN) and Evolving Type 2 Quantum Fuzzy Neural Network (eT2QFNN) structures have been developed in this study. These evolving structures can better capture the nonlinear aerodynamic characteristics of the aircraft. Also, they are open to interpretation and they are robust to model uncertainties. The aerodynamic postulate model obtained from this methodology is compared with the aerodynamic postulate models obtained by OLS, NN, and ANFIS structures and the accuracy of the obtained aerodynamic models is analyzed. Firstly, flight data from the flight test campaign previously conducted with the ATTAS aircraft are used to obtain the aerodynamic model of the ATTAS aircraft. When selecting the suitability of this flight data, attention should be paid to whether the aircraft can trigger the longitudinal, lateral and directional modes. In this study, short period, bank to bank and dutch roll maneuvers were used to trigger the longitudinal, lateral and directional modes of the ATTAS aircraft. With these maneuvers, the responses of the aircraft obtained from the sensor were analyzed and the parameters to be used in system identification were recorded. A low-pass filter was used to remove noise from the recorded flight data. Thus, the noise effect in the parameters to be used in the identification of the aerodynamic model of the ATTAS aircraft was removed and made more appropriate. After the obtained flight data were filtered with a low-pass filter, the flight data was preprocessed. In order to preprocess the data, force and moment equations were generated in MATLAB using the weight, moment of inertia, and thrust values of the ATTAS aircraft. Then, the linear accelerations and angular rates obtained from the measured flight data are written into the previously created equations, and the aerodynamic force and moment coefficients are calculated. Thus, reference aerodynamic coefficients expressing the characteristics of the ATTAS aircraft are calculated with these flight data. After obtaining the reference aerodynamic coefficients, the aerodynamic postulate model of the ATTAS aircraft is derived. While constructing this postulate model, the aerodynamic postulate models available in the literature and the stepwise regression algorithm are utilized. With the stepwise regression algorithm, it was determined which stability and control derivative coefficients can be used in the aerodynamic postulate model and the over-parameterization problem was avoided. As a result of these analyses, the postulate models were obtained for 6 aerodynamic coefficients. In the next step, it is aimed to obtain aerodynamic postulate models that can represent the aerodynamic characteristics of the ATTAS aircraft well by using system identification algorithms. These models are compared with the reference models obtained from the force and moment equations to analyze whether they accurately represent the aerodynamic characteristics of the ATTAS aircraft. In this study, eT1QFNN and eT2QFNN are proposed to model the aerodynamic characteristics of the ATTAS aircraft. These evolving structures, which contain quantum fuzzy sets and neural network structures, have multiple inputs and a single output. In these evolving structures, the learning process starts with an empty rule base and the structure is continuously updated as a new data sample arrives. With each new data sample, these evolving structures generate a hypothetical rule that drives the autonomous evolution of the fuzzy rules. The generated hypothetical rules need to evolve significantly before they are incorporated into the network structure. The significance is evaluated using the Gaussian Mixture Model to predict complex changes in the data. If the generated hypothetical rules provide more contribution and meaning than the existing rules, they are added to this structure as new rules. On the other hand, when the hypothetical rules do not provide more meaning than the existing rules, the parameters of the quantum membership function and the consequent weight parameters in the rule base are updated by a decoupled extended Kalman filter. To do this, a winning rule is developed that depends on the maximum spatial firing power. In other words, the antecedent membership function and consequent weight parameters of the rule with maximum spatial firing power are updated. Thus, the performance of the evolving structures is preserved. These evolving structures are robust to uncertainties and data noise thanks to quantum membership functions as well as automatic rule learning and parameter tuning capabilities. They can also represent the nonlinear aircraft model by creating multiple linear sub-models with a rule-based structure through an incremental learning strategy instead of the traditional batch learning approach. In the next step of the study, the aerodynamic postulate models obtained from the proposed eT1QFNN and eT2QFNN are compared with the aerodynamic postulate models obtained from the OLS, NN, and ANFIS structures. Thus, the proposed methodology can be compared with previously existing methodologies in the literature in terms of modeling performance. In order to examine whether the system identification algorithms can successfully represent the aerodynamic characteristics of the ATTAS aircraft, two different settings were made. In the first one, training was performed with 80% of the flight data and testing with 20% of the flight data, while in the second one, training was performed with 50% of the flight data and testing with 50% of the flight data. Thus, models trained with both large and small data sets were analyzed. Furthermore, it was questioned whether the aerodynamic characteristics of the ATTAS aircraft could be captured with less flight data. In addition, during the training process of ANFIS and NN based aerodynamic models, overfitting was checked using test data. In contrast, no such overfitting check was performed for the OLS, eT1QFNN, and eT2QFNN models. This distinction arises from the fact that ANFIS and NN models are trained through multiple iterations, whereas OLS, eT1QFNN and eT2QFNN models are trained in a single iteration. In the next phase of the study, the Delta method was applied to the aerodynamic models estimated with the eT1QFNN and eT2QFNN with more training data, since more training data included short period, bank to bank, and dutch roll maneuvers. Thus, all longitudinal, lateral, and directional modes of the ATTAS aircraft could be triggered. As a result of the application of this method, the control and stability derivative parameters of the aerodynamic model were obtained. The dynamics, stability and controllability of the aircraft could be analyzed using these parameters. In this study, the control and stability derivative parameters are obtained by perturbing each of the input variables by about 1% in each direction. While one input variable is perturbed, the others should remain constant. The values of the control and stability derivative parameters during the flight time are shown and analyzed in histogram plots. The structure and sensitivity of the evolving structures in the rule bases could be interpreted by looking at the changes of these parameters in the histogram plots. The parameters obtained from this evolving structure with the Delta method were compared with the parameters obtained from the OLS method. Thus, it was analyzed whether the control and stability derivative parameters obtained from the evolving structure consistently represent the aerodynamic characteristics of the ATTAS aircraft. As a result, when the aerodynamic models obtained with the eT1QFNN and eT2QFNN are compared with the aerodynamic models obtained with other system identification algorithms, it is seen that the eT2QFNN better represents the aerodynamic characteristics of the ATTAS aircraft. In making this comparison, the closeness of the obtained aerodynamic postulate model to the reference aerodynamic model obtained in the flight test was considered. In addition, the accuracy of the values of the control and stability derivative parameters of the aerodynamic postulate model was also analyzed.M.Sc
Collective leadership: Leader of halay / sergovend
No full textTez (Yüksek Lisans)-- İstanbul Teknik Üniversitesi, Lisansüstü Eğitim Enstitüsü, 2025Tezin ana konusu, geleneksel halay dansları çerçevesinde Diyarbakır yöresindeki halaylarda "halay başı / sergovend" rolü ve bu rolün kolektif liderlik dinamikleri ile ilişkisini incelemektir. Çalışmada, halay başının performansındaki rolü ve bu rolün halayın kolektif dinamiği üzerindeki etkileri araştırılmıştır. Tezin amacı, Diyarbakır özelinde halay danslarının içindeki liderlik özelliklerini ve halay başının bu bağlamdaki işlevini analiz etmektir. Ayrıca, geleneksel dansların öğretiminde uygulanacak yöntemler ve bu bağlamda sahneleme yaklaşımının nasıl olabileceğine dair öneriler sunmak, araştırmanın hedefleri arasında yer almaktadır. Halay başı olma isteği ve bu isteğin arkasındaki sosyal dinamiklerin anlaşılması, bu tez çalışmasının önemli bir başka yönüdür. Tezde halaylar, Diyarbakır'da düğünler başta olmak üzere, sosyal etkinlikler, On Gözlü Köprü gibi kültürel mekanlar, yarışma, BÜFK ve BGST gibi farklı sahneleme anlayışları üzerinden incelenmiştir. Diyarbakır'da yapılan saha araştırmalarındaki gözlem ve görüşmeler, halayların nasıl bir topluluk dinamiği oluşturduğunu ve katılımcıların sosyal etkileşimlerini nasıl etkilediğini anlamaya yardımcı olmuştur. Özellikle halayların kadın-erkek grupları içerisinde ve farklı mekânlarda nasıl icra edildiği, bu ritüel ve sosyal yapı içerisindeki bireylerin rollerinin ve kimliklerinin nasıl şekillendiği üzerinde durulmuştur. Çalışmada, geleneksel ortamlarda, modern düğünlerdeki dans geçişleri, müziğin ve halay başının rolü gibi unsurlar analiz edilmiştir. Bu bağlamda, katılımcıların dans sırasında etkileşimleri, halay başının liderlik özellikleri ve sosyal motivasyonları incelenmiştir. Ayrıca çocuk halay başları üzerinden, çocukların halayları öğrenme süreçleri ve gelenekler arasında nasıl bir bağ kurulabileceği de örnek olarak gösterilmiştir. Çocuk halay başları üzerindeki örneklemler, halayların aktarım süreçlerinin anlaşılmasına katkı sağlamıştır. Tezde beceri, halay başı liderliğinin önemli bir bileşeni olarak tanımlanmaktadır. Halay başının, grup içindeki performansı ve liderlik rollerini etkileyen bazı spesifik becerilere sahip olması gerektiği vurgulanmaktadır. Bu bağlamda beceri, sadece dansın icrasındaki fiziksel becerilerle sınırlı kalmayıp aynı zamanda sosyal etkileşim, iletişim ve grup dinamiklerini yönetme becerileri olarak geniş bir çerçevede ele alınmaktadır. Halay başının performans dinamikleri, grup motivasyonu ve grubun enerjisini yönlendirme kabiliyeti "Akış" kuramı üzerinden incelenerek analiz edilmiştir. Akış kuramı üzerinden yapılan incelemenin; 'dans terapisi', 'psikoloji ve dans' gibi farklı alanlara fikirler sunacağı ve çalışmalara alan yaratacağı düşünülmektedir. Bu tez çalışmasının halay dışındaki farklı dans disiplinleri üzerine de, baş dansçı, dansta liderlik, solo performans, dansta doğaçlama ve grup dinamiklerinin incelenmesi üzerine fikirler sunabileceği, daha geniş kapsamlı çalışmalara evrilebileceği öngörülmektedir. Halay başı, grubun enerjisini yönlendirme, katılımcıları motive etme ve kolektif psikolojiyi yönetme kabiliyeti ile öne çıktığı için bu liderlik becerisi, toplumsal ihtiyaçlar doğrultusunda kendini gösterebilmektedir. Bu nedenle, halay başı performansının toplumda nasıl bir değer yaratabileceği ve bu performansların profesyonelleşme durumu da araştırma kapsamındadır. Bu çalışmanın sadece geleneksel dans literatürüne değil, aynı zamanda liderlik, iletişim, grup dinamikleri ve akış deneyimi alanlarına da katkı sağlayacağına inanılmaktadır.Yüksek Lisan
Çeşitli geçiş metalleri ile sentezlenen alaşımların dikey yönelimli karbon nanotüp katalizi olarak kullanımının incelenmesi
No full textThesis (Ph.D.) -- Istanbul Technical University, Graduate School, 2025A novel form of carbon, buckminsterfullerene C60 was discovered in 1985 by Kroto, Smalley, and their colleagues. This invention awarded them the Nobel Prize in chemistry in 1997. Pure carbon atoms bond in the shape of hexagons and pentagons to form the soccer-ball-like molecule C60. Besides well-known forms of carbon atoms such as diamond, C60, and graphite, carbon nanotubes (CNTs) were discovered in 1991 by Iijima. First, he found multiwall carbon nanotubes (MWCNTs) in the carbon soot synthesized by an arc discharge method. Two years later, he observed the single-wall carbon nanotubes (SWCNTs). Since then, nanotubes have attracted the interest of scientists worldwide due to their exceptional physical and chemical characteristics. They have been recognized with higher mechanical, thermal, and electrical properties that have never been seen in a material before. Because of these properties, nanotubes are the ideal material for various applications, including basic science research. Theoretical and experimental studies have shown that CNTs have exceptional mechanical properties, a high aspect ratio (~104), excellent waviness characteristics, high thermal properties (2000-6000 W/m K), good electrical conductivity (106 to 107 S/m), low density (1.3-1.4 g/cm3), excellent hydrogen storage, high corrosion resistance, and unique optical properties. Due to their unique characteristics, CNTs have triggered a big interest among mainstream researchers. They are now considered to be the most promising material used in nano-electronics, energy storage devices, composite materials, the medical field, nano-sensor applications, and so on. Although it has the aforementioned great qualities, the low-quality batch synthesizing of CNTs with smaller diameters and non-selective chirality growth of CNTs remains to restrict the application of CNTs in demanding applications such as electronics, supercapacitors, and sensors. Even though vertically aligned carbon nanotubes (VACNTs) can be grown with transition metals like Fe, Ni, Mo, and Cu, it remains difficult to synthesize fully aligned CNTs with low defect counts, high quality, and homogeneous and controlled chirality specifically for electronic applications. A recent study revealed that bimetallic catalysts offer the potential for size control, quality enhancement, and chirality distribution. Many experimental variables such as carbon source (CO, C2H4, C2H2, CH4, etc.), catalyst particle type (monometallic or bimetallic), the feedstock flux, the support materials (SiO2, Al2O3, etc.) surface treatments (chemical etching, ion bombardment, etc.), reaction time, and temperatures have been suggested as experimental variables for the controlling CNT diameter. The control of the tube diameter, which will directly impact the chiral distribution, is still a hurdle due to the enormous number of variable combinations. In Chapter 3, detailed information about VACNTs synthesized on different catalyst particles was given with the synthesis method and characterization. First, VACNTs were synthesized on pure Fe with standard protocol by catalytic chemical vapor deposition (CCVD). Then, they were characterized by Raman spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) to identify IG/ID ratio with both single point and mapping, the purity and decomposition, the direction of VACNTs, the surface area of VACNTs, the crystallinity, sp2: sp3 ratio and determination of all elements in the structure. For the growth of VACNTs, different catalyst particles, such as Fe-Ni and Fe-Mo, with varying weight fractions were prepared using the mechanical alloying (MA) method. These catalyst particles were then pressed into bulk form and characterized by X-ray powder diffraction (as detailed in Chapter 3). The prepared catalysts were subsequently coated onto silicon wafers with the desired thickness using the electron beam evaporation method. Following this step, VACNTs were synthesized on the coated Si wafer using catalytic chemical vapor deposition (CCVD) with a standard recipe. For each catalyst particle, the structural characterization of VACNTs was conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine the alignment of the CNT, innermost and outer diameters, and the number of walls. Furthermore, Raman spectroscopy was employed to analyze CNT chirality, chirality distribution, IG/ID mapping, and defect density. Additionally, thermogravimetric analysis (TGA) was used to assess the purity and decomposition behavior of VACNTs concerning different catalyst particles. Studies have shown that the addition of nickel and molybdenum enhances the quality of VACNTs. Moreover, it has been reported that incorporating nickel and molybdenum into iron alters the chirality of CNTs. Additionally, the water-assisted chemical vapor deposition (WA-CVD) system was established at ITU-ARC (Chapter 3). Extensive experiments were conducted to achieve the maximum length of VACNTs. According to the results, VACNTs synthesized via WA-CVD reached an approximate height of 7.6 mm. These findings hold significant potential for applications in nanocomposite materials and the dry spinning of CNTs. In Chapter 4, FeSi was used as a catalyst for the growth of CNTs. In the CCVD system, CNTs were synthesized directly on FeSi powder. All samples were characterized using Raman spectroscopy, SEM-EDS, and TEM to analyze the IG/ID ratio, chemical composition, presence of CNTs on FeSi particles, tube diameter, and number of walls. This chapter elucidates the growth mechanism of CNTs on FeSi particles based on characterization results. Using different synthesis parameters, CNTs were grown on FeSi powder and characterized by SEM. Raman spectroscopy was employed to compare the full-width at half-maximum (FWHM) values of the G and D peaks. Additionally, the defect distance (Lᴅ) and defect density (nᴅ) were calculated for each sample. The magnetic properties of CNT-doped FeSi samples synthesized with different recipes, as well as FeSi powder, were measured at 10 K and 300 K using a vibrating sample magnetometer (VSM). According to the results, the average magnetic saturation of FeSi powder was measured as 20 emu/g at 10 K. For the FeSi-1000-CNT and FeSi-500-CNT samples, magnetic saturation values at 10 K were 14.8 emu/g and 11.5 emu/g, respectively. At 300 K, the measured average magnetic saturation values were 15.4 emu/g, 12.8 emu/g, and 9 emu/g for FeSi, FeSi-1000-CNT, and FeSi-500-CNT samples, respectively. Raman spectroscopy results indicated that as the CNT content increased, the decomposition of iron within the powder led to a decrease in magnetic saturation. This observation was further supported by SEM-EDS and TEM analyses. In Chapter 5, CNT-reinforced polymer matrix nanocomposites (PNCs) were fabricated using different polymer types and various weight fractions. The dynamic mechanical properties of these PNCs were analyzed based on polymer type, CNT volume fraction, CNT alignment, and temperature effects. The study presents the production of both randomly oriented and aligned CNT-PNCs, examining their dynamic mechanical behavior at different temperatures. The morphological characterizations of these composites are provided and compared to assess the impact of CNT alignment and dispersion on their mechanical performance. This thesis investigates the effects of different catalyst types and concentrations on VACNT properties, a topic not previously explained together in the literature. Additionally, CVD and WACVD systems were established and used for various studies at İTÜ ARC. VACNT production was carried out using different catalysts, and the impact of catalysts on the morphological and chemical properties of VACNTs was reported. Furthermore, CNT-reinforced PNCs were produced using various polymers, and their dynamic mechanical properties were analyzed based on CNT orientation and volume fraction at different temperatures using dynamic mechanical analysis.Ph.D
Kaynak kıtlığı çağında psikolojik iyi oluş: Zaman ve para bağışlama davranışlarının bir analizi
No full textThesis (Ph.D.) -- Istanbul Technical University, Graduate School, 2025One of the inevitable realities individuals face in their daily lives is having limited resources. This situation, referred to as resource scarcity, can be defined as having fewer resources than needed to meet one's needs and wants. The resource scarcity encountered by individuals can be assessed on both macro and micro levels. On a macro level, the scarcity of water and food supply due to high levels of drought in various regions of the world can be considered resource scarcity. On a micro level, individuals may feel pressure due to limited financial income to meet personal needs and time constraints on daily activities. This thesis focuses on micro-level resource scarcity, emphasizing individuals' perceptions of time and money as scarce resources. It is clear that a multitude of factors influence consumer behavior. Previous studies have shown that consumer behavior is shaped by individual, situational, economic, psychological, sociological, and other factors. In these studies, resource scarcity has been considered a factor affecting consumer psychology and behavior, revealing its impacts on individuals' cognitions, attitudes, and behaviors. It is known that individuals with limited resources experience increased stress levels, feel negative emotions, and generally have decreased life satisfaction. Resource scarcity adversely affects consumers' decision-making processes, leading to observable changes in their cognitions. Moreover, when faced with resource scarcity, consumers are known to use their existing resources more consciously and experience a fear of missing out. While engaging in consumption activities for themselves, individuals also allocate resources for those in need and to improve societal welfare. When considered consumer behavior, this behavior, termed donating or charitable giving, highlights the importance of understanding the role of resource scarcity in donation behavior. Individuals tend to donate by giving money and time to nonprofit organizations providing access to aid products or services to needy people. The fact that time and money, the two primary sources of giving behavior for today's individuals, are limited resources reveals the importance of resource scarcity on giving behavior. Time and money are perceived differently by individuals due to their various characteristics. For instance, money is more accessible to count, save, and touch than time. While time is associated with an emotional mindset in consumers' minds, money is related to a financial value-based mindset. When examined within the framework of construal level theory, money is perceived concretely by individuals, whereas time is perceived abstractly. However, considering that resource scarcity affects cognitive processes, it is crucial to understand how perceptions of time and money differ during donation compared to situations where scarcity is not felt. Given that individual donors predominantly make donations to nonprofit organizations understanding the perceptions of scarce resources like money and time during the donation process can provide insights into how relevant organizations should approach their current and potential donors. Regardless of the amount of resources individuals possess, individual and organizational factors affect donation behavior. Some of these factors are the perceived donation efficacy and organizational trustworthiness. Since scarce resources are attributed greater value by individuals, organizations' trustworthiness and perceived donation efficacy gain importance when these resources are donated. Additionally, donating scarce resources with greater attributed value makes donors feel better about themselves. This study examines trust in the institution and perceived donation effectiveness as variables affecting the relationship between psychological well-being and donation intention. This thesis employed experimental design and in-depth interviews to answer the research questions. Study 1a investigates how donors perceive money and time within the framework of construal level theory in situations without any scarcity manipulation. Study 1b explores how donors exposed to resource scarcity manipulation perceive money and time. Study 2 focuses on the psychological well-being levels obtained by individuals donating their scarce resources. It reveals the difference in psychological well-being levels obtained based on the type of resources donated. Study 3 examines the moderating effect of organizational trustworthiness and perceived donation efficacy on the relationship between the psychological well-being levels of individuals donating their scarce resources and their donation intentions. Through in-depth interviews, the aim was to identify the reason behind the insignificant moderating effect of organizational trustworthiness and perceived donation effectiveness on the relationship between psychological well-being levels and donation intentions. The results indicate that without a scarcity reminder, donors perceive time on an abstract level and money on a concrete level. When exposed to resource scarcity manipulation, the level of abstraction in perceiving time and money increases.Ph.D
Makine öğrenimi tekniklerini kullanarak inşaatta risk tabanlı maliyet tahmini
No full textThesis (Ph.D.) -- Istanbul Technical University, Graduate School, 2025The construction industry is one of the sectors that experiences frequently cost overruns. Therefore, precise cost estimation for the completion of construction projects is essential. Several research studies focus on cost estimation, construction risk parameters, and their monetary effects. While they developed significant predictive models for project completion costs, they mainly focused on the initial construction phases. Estimating the completion cost accurately in the early phases of construction projects is critical to their success. However, cost overruns are almost inevitable due to the risks inherent in construction projects. Hence, the completion cost fluctuates throughout the execution phase and requires periodic updates. Limited studies have developed methodologies for estimating completion costs throughout the execution phase of projects. However, their models do not incorporate the implications of total risk scores. Further study is required to examine risk-based cost prediction for completion throughout the construction execution phase. There is a need for a prompt and user-friendly completion cost estimation model that accounts for fluctuating risk scores and their impact on the total cost during the execution phase. Machine learning (ML) techniques could address these requirements by providing effective methods for tackling dynamic systems. The proposed approach includes ML prediction and classification models to estimate total completion cost and cost overrun percentage class of the project, respectively. Within the predictive models, six predictive algorithms were utilized, employing machine learning techniques. Analysis of the outputs revealed that polynomial regression yielded the most precise predictions for the supplied data from globally operating construction company. The classification approach aims to predict the cost overrun ratio classes of the completion cost according to the changes in the total risk scores at any time of the project. Six classification algorithms were utilized and validated by employing data points from a globally operating construction company. The performances of the algorithms were evaluated with validation and performance indices. The decision tree classifier surpassed other algorithms. The main objective of this study is to provide a system that predicts the total completion cost and/or cost overrun percentage classification based on the total risk score of projects at any point of the execution phase. Although there are some research limitations, including risk perception, data gathering restrictions, and selecting proper ML algorithms upon data properties, this research improves the planning abilities of construction executives by providing completion cost and cost overrun ratio based on changing total risk scores, facilitating swift and simple assessments at any stage of a construction project's execution.Ph.D
Optimization of mechanical alloying of CoCrFeNiAlx (x=0.2; 0.6; 1.0; 1.5) high entropy alloy systems and investigation the effect of B4C addition on spark plasma sintering process
No full textTez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Lisansüstü Eğitim Enstitüsü, 2025Yüksek entropili alaşımlar (YEA), en az beş farklı elementin yapıya dahil olmasıyla elde edilen malzeme grubudur. Alaşım sisteminde bulunan, veya eklenecek olan her bir elementin, malzemenin belirli özelliklerini geliştirmesi beklenir. Mevcut alaşıma, çeşitli takviye malzemeleri (bor karbür, silisyum karbür vb.) veya oranı %5'ten daha az olacak şekilde minör olarak adlandırılan alaşım elementleri de eklenerek, yüksek mukavemet, yüksek sertlik, yüksek aşınma direnci, iyi seviyede korozyon ve oksidasyon direncine sahip bir malzeme elde edilebilmektedir. Bu sayede, yüksek entropili alaşım sistemlerinin, üstün performans gerektiren çeşitli alanlara yönelik (havacılık, otomotiv vb.) geliştirilmesine devam edilmektedir. YEA sistemlerinin kendine has bazı özellikleri bulunmaktadır. Bu özellikler, dört temel etki olarak adlandırılmakta olup, yüksek entropi etkisi, yüksek latis distorsiyonu, yavaş difüzyon etkisi ve kokteyl etkileridir. İlgili parametreler sayesinde, malzemelerin temel özellikleri ve davranışları hakkında bilgi edinilebilmektedir. YEA sistemlerinde en çok kullanılan üretim yöntemleri, genellikle üç başlık altında değerlendirilmektedir. Bu yöntemler; katı hal, sıvı hal ve gaz hal olmak üzere sınıflandırılmaktadır. Sıvı hal yöntemlerinde en çok kullanılan vakum ark ergitme prosesidir. Bu yöntemin temel sınırlaması, homojenliğin elde edilmesinin uzun vakitler gerektirmesidir. Homojenliğin sağlanması için, yöntemin birden fazla kez tekrarlanması gerekebilmektedir. Gaz hal üretim yöntemleri, genellikle YEA film kaplamaları üretiminde tercih edilmektedir. Katı hal üretim yöntemlerinde ise mekanik alaşımlama (MA) prosesi yer almaktadır. Mekanik alaşımlama prosesinde, toz, bilye ve proses kontrol maddesinin içerisinde olduğu, genellikle paslanmaz çelikten oluşan bir kap sistemi kullanılır. Yüksek enerjili değirmenlerde gerçekleştirilen proseste, çarpışmanın kuvvetiyle, toz parçacıkları plastik olarak deforme olur ve deformasyon sertleşmesine uğrayıp ile parçacıkların kırılması sağlanır. MA sayesinde, vakum ark ergitme yönteminin sınırlamalarından olan homojen mikroyapı iyi bir şekilde elde edilebilmektedir. Malzemede istenen yoğunluğun elde edilebilmesi için, MA işlemini takiben spark plazma sinterleme ile malzemeler şekillendirilerek, yüksek yoğunluk değerleri elde edilebilmektedir. SPS işlemi, düşük voltajlı, doğru akımlı, darbeli akımla aktive edilen bir basınçlı sinterleme tekniği olarak da bilinir ve yüksek sıcaklıklarda bile malzemelerin çok kısa sürelerde sinterlenip, yoğunlaştırılması sağlanır. YEA sistemlerine takviye malzemesi olarak eklenebilen, bor karbür (B4C), elmas ve kübik bor nitrürün ardından bilinen en sert üçüncü malzemedir. Bor karbür, düşük yoğunluğu (2,52 g/cm3), yüksek sertliği (29.1 GPa), yüksek ergime sıcaklığı (2450°C), yüksek elastik modülü (448 GPa), yüksek nötron emilim kesiti (600 barns) ve mükemmel termoelektrik gibi birçok çekici kombinasyonu sebebiyle yüksek performans uygulamaları için uygun bir malzemedir. Bu kapsamda, bor karbür, nükleer endüstride, personel ve araç güvenliği için zırh, roket yakıtı vb. uygulamalarda kullanılmaktadır. Çalışma kapsamında CoCrFeNiAlx (x=0,2 0,6 1,0 1,5) yüksek entropili alaşım sistemleri, mekanik alaşımlama yöntemi ile farklı sürelerde (2, 4, 6 ve 8 saat), sabit rpm dönüş hızında (800) üretilmiştir. Üretilen toz alaşımının partikül boyut dağılımları belirlenmiş ve X-ışını difraktormetre analizi (XRD) ile faz analizleri gerçekleştirilmiştir. Sinterleme işleminden önce, ThermoCalc yazılım programında yapıda hangi fazların oluşabileceğine ilişkin faz tahmin analizi gerçekleştirilmiştir. MA yöntemiyle üretilen toz alaşımlarının şekillendirilmesi için spark plazma sinterleme (SPS) prosesi gerçekleştirilmiştir. Sinterleme işleminde başlangıç tozu olarak 20 saat 300 rpm hızında öğütülmüş CoCrFeNiAl0,2 ve CoCrFeNiAl1 alaşım sistemleri kullanılmıştır. Bor karbür takviyeli alaşım sistemlerinde, sinterleme işleminden önce, öğütülmüş YEA tozları ve bor karbürün daha iyi homojen dağılımı için turbulada 6 saat süreyle karıştırma işlemi gerçekleştirilmiştir. Bu kapsamda, hem takviyesiz hem de değişen oranlarda (hacimce %2 ve %4) bor karbür takviyeli CoCrFeNiAl0,2 ve CoCrFeNiAl1 alaşım sistemleri değişen sıcaklıklarda (845, 900, 1000°C), sabit basınçta (40 MPa) ve sabit sinterleme sıcaklığında (3 dakika) SPS yöntemiyle şekillendirilmiştir. SPS işlemlerinden sonra, malzemelerin yoğunluk ölçümleri, XRD yöntemiyle faz analizleri, taramalı elektron mikroskobu ve enerji dağılım spektrometresi ile mikroyapı karakterizasyonları gerçekleştirilmiştir. Mekanik testler kapsamında, malzemelerin Vickers mikrosertlik ölçümleri, aşınma ve basma testleri yapılmıştır. Malzemelerin termal davranışları hakkında bilgi sahibi olabilmek için termogravimetrik analiz (TGA) ve diferansiyel termal analiz (DTA) işlemleri gerçekleştirilmiştir. Partikül boyut analizlerinde, genellikle 2-4 saat aralığında partikül boyutlarında bir azalma görülmüştür. Burada mekanik alaşımlama mekanizmalarından kırılma, soğuk kaynağa göre daha baskındır. 4-6 saat aralığında ise partikül boyutlarında bir artış görülmüştür. Burada ise soğuk kaynağın kırılmaya göre baskın olduğu gözlemlenmiştir. En yüksek yoğunluk değeri (7,87 ± 0,012), 1000°C sıcaklık, 40 MPA basınç ve 3 dakika sinterleme süresinde sinterlenen CoCrFeNiAl0,2 sisteminde elde edilmiştir. Yoğunluk artışının temel sebebinin, sinterleme sıcaklığındaki artışa bağlı olarak por miktarının azalması ve alüminyum oranının düşük olmasından kaynaklandığı görülmüştür. Mekanik alaşımlanmış CoCrFeNiAlx sistemlerinin faz analizlerine bakıldığında tüm alüminyum içeriğinde, YMK ve HMK katı çözeltilerinin bir arada bulunduğu görülmüştür. Elde edilen bu sonuçların termodinamik hesaplamalarla da uyumlu olduğu görülmüştür. Sinterlenmiş numunelerin faz analizlerine bakıldığında ise, eşmolar alaşım sistemlerinin hepsinde YMK ve HMK fazları bir arada bulunurken, ek olarak alüminyum esaslı intermetalik bileşiğin ve işlemler sırasında karbon difüzyonuna bağlı olarak karbürlü yapılarının da bulunduğu görülmüştür. Eşmolar olmayan CoCrFeNiAl0,2 alaşım sistemlerinde ise ağırlıklı olarak YMK katı çözelti fazı ve karbürlü yapılar mevcuttur. Alüminyum oranının arttıkça, tek fazlı bir HMK yapısının oluşacağı bilinmektedir. Dolayısıyla eşmolar olmayan CoCrFeNiAl0,2 sisteminde alüminyum oranının düşük olmasına bağlı olarak ağırlıklı olarak YMK fazının bulunması beklenen bir durumdur. Taramalı elektron mikroskobu ve enerji dağılım spektrometresi ile yapılan mikroyapı karakterizasyonlarıyla, X-ışını difraktormetre analizi sonuçlarının birbiriyle uyumlu olduğu görülmüştür. En yüksek sertlik değeri (4,76 ± 0,17 GPa), 900°C sıcaklıkta – 40 MPa basınçta – 3 dakika sinterleme süresinde sinterlenen takviyesiz CoCrFeNiAl alaşımında elde edilmiştir. Genel olarak, yoğunlaşmanın daha iyi olduğu sıcaklıklarda bor karbür takviyesiyle birlikte sertlik değerleri, takviyesiz sisteme göre eşdeğerdir. En yüksek sinterleme sıcaklığında (1000°C) ise, B4C takviyesiyle birlikte, sertlik değerinde belirgin bir artış görülmüştür. Bunun sebebinin, yüksek yoğunlaşmaya ek olarak, takviyesiz sisteme göre farklı pik açılarında oluşan Fe,Cr esaslı karbür yapılarından kaynakladığı düşünülmektedir. Aşınma testi sonuçlarına göre, 845 ve 900°C'de B4C ilavesiyle, daha düşük aşınma derinliği ve genişliğiyle birlikte ortalama sürtünme katsayısı, hacimsel aşınma kaybı ve spesifik aşınma hızı değerleri azalarak aşınma direncinde iyileşme elde edilmiştir. 1000°C sıcaklıkta ise, B4C ilavesiyle birlikte daha yüksek sürtünme katsayısı, hacimsel aşınma kaybı ve aşınma hızı elde edilmiştir. Bunun sebebinin malzeme yüzeyinde oksit tabakasının meydana geldiği düşünülmektedir. Elde edilen verilerin, profilometre sonuçlarıyla ve optik mikroskop görüntüleriyle uyumlu olduğu görülmüştür. Basma testleri, en yüksek sertlik değerine sahip 900°C sıcaklıkta sinterlenen takviyesiz CoCrFeNiAl alaşımı ve en yüksek yoğunluk değerine sahip 1000°C sıcaklıkta sinterlenen eşmolar olmayan takviyesiz CoCrFeNiAl0,2 alaşım sisteminde gerçekleştirilmiştir. Eşmolar olmayan alaşım sisteminin basma mukavemeti 1388,19 MPa bulunurken, eşmolar alaşım sisteminin ise 395,62 MPa bulunmuştur. Sinterleme sıcaklığının artışıyla beraber basma mukavemeti değerinde de artış görülmüştür. Basma mukavemetindeki artışın, azalan gözenek miktarı ve gözenek boyutuna bağlı olarak gerçekleştiği düşünülmektedir. Termal testler kapsamında, en yüksek sertlik değerine sahip 900°C sıcaklıkta sinterlenen takviyesiz CoCrFeNiAl alaşımı ve %2 bor karbür takviyeli sistemleri için termogravimetri (TG) ve diferansiyel termal analizleri (DTA) gerçekleştirilmiştir. Bu kapsamda her iki alaşım için parabolik hız sabitleri hesaplanmıştır. Takviyesiz alaşımın parabolik hız sabiti, kp=1.21×10−8 (mg²/cm⁴/s), bor karbür takviyeli alaşımın parabolik hız sabiti değeri ise kp≈1.71×10−9 (mg²/cm⁴/s) olarak bulunmuştur. Her iki sistemde de ağırlık artışının az olduğu (takviyesiz sistemde %0,7 takviyeli sistemde ise %0,3) ve parabolik hız sabiti değerlerinin düşük olması sebebiyle oksidasyona karşı iyi bir dirence sahip oldukları söylenebilir. B4C ilavesinin, daha az ağırlık artışına ve hız sabiti değerinin daha düşük olmasına sebep olarak, oksidasyon direncini iyileştirmiştir.Yüksek Lisan
Modelling glass forming using computational fluid dynamics
No full textTez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Lisansüstü Eğitim Enstitüsü, 2025Cam üretim prosesinde yüksek miktarda enerji ve hammadde kullanılmaktadır. Enerji kaynağı olarak fosil yakıtlar başta olmak üzere ek olarak da düşük miktarda yenilenebilir kaynaklara ihtiyaç duyulmaktadır. Hem emek hem de enerji yoğun olan bu sektörde, verimliliklerin en üst noktada tutulması firmaların pazarda rekabet şansını arttırmaktadır. Günümüz dünyasında enerji kaynaklarının tükenmesi nedeniyle kullanılacak tüm girdilerden en üst seviyede faydalanmak, şirketlerin ayakta kalması açısından yararlı olacaktır. Son zamanlarda yaşanılan enerji ve hammadde krizleri sebebiyle de şirketler, kaynaklarını doğru bir şekilde yönetmenin yollarını aramaktadır. Bu çalışmanın amacı, pres ve pres-üfleme prosesleri ile sofra camı üretiminde yapılan deneme sürelerinin kısaltılması, deneme sayılarınn azaltılması ve ürün gramajlarının optimize edilmesidir. Camın makine ortamında şekillendirilmesi, bilgisayar ortamında modellenerek prosesi etkileyen parametrelerin anlaşılması da hedeflenmiştir. Deneme imalatlarının modellenmesi ve çözümü, bilgisayar ortamında gerçekleştirilerek istenen kalitede ve en uygun gramajda ürün elde edilmesinin yanında, yeni ürünün seri imalata geçiş süresi mevcut duruma göre 8 hafta kısaltılabilmektedir. Ayrıca imalat hatlarındaki deneme kaynaklı duruşların ve deneme maliyetlerinin ortadan kaldırılması hedeflenmektedir. İlave olarak, yapılacak analizler ile üründe istenilen cidar kalınlığını öngörmek ve imalat sırasında meydana gelen ağızda çapak, yarım ağız, dip kayığı ve mastör-cam yapışması gibi imalat hatalarının önüne geçilmesi amaçlanmıştır. Bu proje kapsamında, imalatı yapılan bir üründe kaliteyi arttıracak ve maliyeti düşürecek cidar inceltme, ürün gramajı düşürme, uygun parizon tasarımı vb uygulamaların bir Hesaplamalı Akışkanlar Dinamiği (HAD) yazılımı ile önceden belirlenip gerekli çalışmaların hayata geçirilmesi hedeflenmektedir. Aynı zamanda, yeni bir ürünün üretilebilirliğinin HAD sayesinde iki veya daha fazla deneme yapılmadan anlaşılabilmesi planlanmaktadır.Yüksek Lisan
Development of BaSrTiO3 nanomaterial based dispersive solid phase microextraction method for cadmium determination in thyme samples using flame atomic absorption spectrometry
No full textThis study presents an efficient and straightforward approach for the easy synthesis and innovative analytical application of an industrial nanomaterial of BaSrTiO(3) (BST). Characterization techniques including XRD (X-ray Diffraction), FTIR (Fourier transform infrared spectroscopy), and SEM (scanning electron microscopy) were utilized for characterizing the synthesized nanomaterial. Subsequently, the incorporation of BaSrTiO(3) nanomaterial-based DSPME (dispersive solid phase microextraction) and FAAS (flame atomic absorption spectrophotometry) was implemented for the preconcentration of Cd with enhanced precision and accuracy. Each variable influencing the outcome of extraction efficiency has been defined in the optimization studies. The limit of quantification (LOQ) and limit of detection (LOD) values for the BaSrTiO(3) (BST)-DSPME-FAAS system were determined to be 1.1 µg/L and 0.33 µg/L, respectively. Recovery examinations were conducted on two different thyme tea samples utilizing multiple calibration methodologies. The calculated percent recovery values from the spiked samples were in the range of 89.2–123%.https://doi.org/10.1038/s41598-025-08464-7http://dx.doi.org/10.1038/s41598-025-08464-
Optimization-Based Estimation of NED Azimuth and Elevation Angles in Electronic Warfare Systems
No full texthttps://doi.org/10.1109/siu66497.2025.1111241
One Optimization Problem with Convex Set-Valued Mapping and Duality
No full textThis study focuses on the formulation and analysis of problems that are dual to those defined by convex set-valued mappings. Various important classes of optimization problems—such as the classical problems of mathematical and linear programming, as well as extremal problems arising in economic dynamics models—can be reduced to problems of this type. The dual problem proposed in this work is constructed on the basis of the duality theorem connecting the operations of addition and infimal convolution of convex functions, a result that has been previously applied to compact-valued mappings. It appears that, under the so-called nondegeneracy condition, this construction serves as a fundamental approach for deriving duality theorems and establishing both necessary and sufficient optimality conditions. Furthermore, alternative conditions that partially replace the nondegeneracy assumption may also prove valuable for addressing other issues within convex analysis.https://doi.org/10.3390/axioms1411081