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ÖgeExperimental investigation of leading edge suction parameter on massively separated flow(Graduate School, 20210510) Aydın, Egemen ; Yıldırım Çetiner, Nuriye Leman Okşan ; 511171150 ; Aerospace Engineering ; Uçak ve Uzay MühendisliğiThe study aims to investigate and understand the Leading Edge Suction Parameter (LESP) application on the massively separated flow. The experiment was done by gathering force data from the downstream flat plate and the visualization of the flow structures is done by Digital Particle Image Velocimetry. The experiments are conducted in free surface, closedcircuit, large scale water channel located in Trisonic Laboratory of Istanbul Technical University's Faculty of Aeronautics and Astronautics. The velocity of the tunnel is equal to 0.1 m/s which results in a 10.000 Reynolds Number. During the experiment, the flat plate at the downstream of the gust generator (plat plate) is kept constant angle of attack and the test cases are selecting to show that the LESP parameter that derived from only one force component works for different gust interaction with the flat plate. As already discussed in the literature, the critical LESP parameter depends on only airfoil shape and its ambient Reynolds Number. Also, the critical LESP number is calculated in literature as equal to 0,05 for plat plate at the 10,000 Reynolds Number. We did not perform an experiment to find critical LEPS numbers as our experiment was done with a flat plate on 10,000 Re. A different angle of attack and different gust impingement combination has been shown that the LESP parameter works even in a highly unstable gust environment. Flow structures around the airfoil leading edge are behaving as expected from the LESP theory (leadingedge vortex separation and unification).

ÖgeImplementation of propulsion system integration losses to a supersonic military aircraft conceptual design( 20211007) Karaselvi, Emre ; Nikbay, Melike ; 511171151 ; Aeronautics and Astronautics Engineering ; Uçak ve Uzay MühendisliğiMilitary aircraft technologies play an essential role in ensuring combat superiority from the past to the present. That is why the air forces of many countries constantly require the development and procurement of advanced aircraft technologies. A fifthgeneration fighter aircraft is expected to have significant technologies such as stealth, lowprobability of radar interception, agility with supercruise performance, advanced avionics, and computer systems for command, control, and communications. As the propulsion system is a significant component of an aircraft platform, we focus on propulsion system and airframe integration concepts, especially in addressing integration losses during the early conceptual design phase. The approach is aimed to be appropriate for multidisciplinary design optimization practices. Aircraft with jet engines were first employed during the Second World War, and the technology made a significant change in aviation history. Jet engine aircraft, which replaced propeller aircraft, had better maneuverability and flight performance. However, substituting a propeller engine with a jet engine required a new design approach. At first, engineers suggested that removing the propellers could simplify the integration of the propulsion system. However, with jet engines for fighter aircraft, new problems arose due to the full integration of the propulsion system and the aircraft's fuselage. These problems can be divided into two parts: designing air inlet, air intake integration, nozzle/afterbody design, and jet interaction with the tail. The primary function of the air intake is to supply the necessary air to the engine with the least amount of loss. However, the vast flight envelope of the fighter jets complicates the air intake design. Spillage drag, boundary layer formation, bypass air drag, and air intake internal performance are primary considerations for intake system integration. The design and integration of the nozzle is a challenging engineering problem with the complex structure of the afterbody and the presence of jet and freeflow mix over control surfaces. The primary considerations for the nozzle system are afterbody integration, boattail drag, jet flow interaction, engine spacing for twinengine configuration, and nozzle base drag. Each new generation of aircraft design has become a more challenging engineering problem to meet increasing military performances and operational capabilities. This increase is due to higher Mach speeds without afterburner, increased acceleration capability, high maneuverability, and low visibility. Tradeoff analysis of numerous intake nozzle designs should be carried out to meet all these needs. It is essential to calculate the losses caused by different intakes and nozzles at the conceptual design of aircraft. Since the changes made after the design maturation delay the design calendar or changes needed in a matured design cause high costs, it is crucial to accurately present intake and nozzle losses while constructing the conceptual design of a fighter aircraft. This design exploration process needs to be automated using numerical tools to investigate all possible alternative design solutions simultaneously and efficiently. Therefore, spillage drag, bypass drag, boundary layer losses due to intake design, boattail drag, nozzle base drag, and engine spacing losses due to nozzle integration are examined within the scope of this thesis. This study is divided into four main titles. The first section, "Introduction", summarizes previous studies on this topic and presents the classification of aircraft engines. Then the problems encountered while integrating the selected aircraft engine into the fighter aircraft are described under the "Problem Statement". In addition, the difficulties encountered in engine integration are divided into two zones. Problem areas are examined as inlet system and afterbody system. The second main topic, "Background on Propulsion," provides basic information about the propulsion system. Hence, the Brayton cycle is used in aviation engines. The working principle of aircraft engines is described under the Brayton Cycle subtitle. For the design of engines, numbers are used to standardize engine zone naming to present a common understanding. That is why the engine station numbers and the regions are shown before developing the methodology. The critical parameters used in engine performance comparisons are thrust, specific thrust and specific fuel consumption, and they are mathematically described. The Aerodynamics subtitle outlines the essential mathematical formulas to understand the additional drag forces caused by propulsion system integration. During the thesis, ideal gas and isentropic flow assumptions are made for the calculations. Definition of drag encountered in aircraft and engine integration are given because accurate definitions prevent double accounting in the calculation. Calculation results with developed algorithms and assumptions are compared with the previous studies of Boeing company in the validation subtitle. For comparison, a model is created to represent the J79 engine with NPSS. The engine's performance on the aircraft is calculated, and given definitions and algorithms add drag forces to the model. The results are converged to Boeing's data with a 5% error margin. After validation, developed algorithms are tested with 5th generation fighter aircraft F22 Raptor to see how the validated approach would yield results in the design of nextgeneration fighter aircraft. Engine design parameters are selected, and the model is developed according to the intake, nozzle, and afterbody design of the F22 aircraft. A model equivalent to the F119PW100 turbofan engine is modeled with NPSS by using the design parameters of the engine. Additional drag forces calculated with the help of algorithms are included in the engine performance results because the model is produced uninstalled engine performance data. Thus, the net propulsive force is compared with the F22 Raptor drag force Brandtl for 40000 ft. The results show that the F22 can fly at an altitude of 40000 ft, with 1.6M, meeting the aircraft requirements. In the thesis, a 2D intake assumption is modeled for losses due to inlet geometry. The effects of the intake capture area, throat area, wedge angle, and duct losses on motor performance are included. However, the modeling does not include a bump intake structure similar to the intake of the F35 aircraft losses due to 3D effects. CFD can model losses related to the 3D intake structure, and test results and thesis studies can be developed. The circular nozzle, nozzle outlet area, nozzle throat area, and nozzle maximum area are used for modeling. The movement of the nozzle blades is included in the model depending on the boattail angle and base area. The works of McDonald & P. Hughest are used as a reference to represent the 2Dsized nozzle. The method described in this thesis is one way of accounting for installation effects in supersonic aircraft. Additionally, the concept works for aircraft with conventional shock inlets or oblique shock inlets flying at speeds up to 2.5 Mach. The equation implementation in NPSS enables aircraft manufacturers to calculate the influence of installation effects on engine performance. The study reveals the methodology for calculating additional drag caused by an engineaircraft integration in the conceptual design phase of nextgeneration fighter aircraft. In this way, the losses caused by the propulsion system can be calculated accurately by the developed approach in projects where aircraft and engine design have not yet matured. If presented, drag definitions are not included during conceptual design causing significant change needs at the design stage where aircraft design evolves. Making changes in the evolved design can bring enormous costs or extend the design calendar.

ÖgeA study on static and dynamic buckling analysis of thin walled composite cylindrical shells(Graduate School, 20220124) Özgen, Cansu ; Doğan, Vedat Ziya ; 511171148 ; Aeronautics and Astronautics Engineering ; Uçak ve Uzay MühendisliğiThinwalled structures have many useage in many industries. Examples of these fields include: aircraft, spacecraft and rockets can be given. The reason for the use of thinwalled structures is that they have a high strength weight ratio. In order to define a cylinder as thinwalled, the ratio of radius to thickness must be more than 20, and one of the problems encountered in the use of such structures is the problem of buckling. It is possible to define the buckling as a state of instability in the structure under compressive loads. This state of instability can be seen in the load displacement graph as the curve follows two different paths. The possible behaviors; snap through or bifurcation behavior. Compressive loading that cause buckling; there may be an axial load, torsional load, bending load, external pressure. In addition to these loads, buckling may occur due to temperature change. Within the scope of this thesis, the buckling behavior of thinwalled cylinders under axial compression was examined. The cylinder under the axial load indicates some displacement. When the amount of load applied reaches critical level, the structure moves from one state of equilibrium to another. After some point, the structure shows high displacement behavior and loses stiffness. The amount of load that the structure will carry decreases considerably, but the structure continues to carry loads. The behavior of the structure after this point is called postbuckling behavior. The critical load level for the structure can be determined by using finite elements method. Linear eigenvalue analysis can be performed to determine the static buckling load. However, it should be noted here that eigenvalueeigenvector analysis can only be used to make an approximate estimate of the buckling load and input the resulting buckling shape into nonlinear analyses as a form of imperfection. In addition, it can be preferred to change parameters and compare them, since they are cheaper than other types of analysis. Since the buckling load is highly affected by the imperfection, nonlinear methods with geometric imperfection should be used to estimate a more precise buckling load. It is not possible to identify geometric imperfection in linear eigenvalue analysis. Therefore, a different type of analysis should be selected in order to add imperfection. For example, an analysis model which includes imperfection can be established with the Riks method as a nonlinear static analysis type. Unlike the NewtonRapson method, the Riks method is capable of backtracking in curves. Thus, it is suitable for use in buckling analysis. In Riks analysis, it is recommended to add imperfection in contrast to linear eigenvalue analysis. Because if the imperfection is added, the problem will be bifurcation problem instead of limit load problem and sharp turns in the graph can cause divergence in analysis. Another nonlinear method of static phenomena is called quasistatic analysis which is used dynamic solver. The important thing to note here is that the inertial effects should be too small to be neglected in the analysis. For this purpose, kinetic energy and internal energy should be compared at the end of the analysis and kinetic energy should be ensured to be negligible levels besides internal energy. Also, if the event is solved in the actual time length, this analysis will be quite expensive. Therefore, the time must be scaled. In order to scale the time correctly, frequency analysis can be performed first and the analysis time can be determined longer than the period corresponding to the first natural frequency. For three analysis methods mentioned within this study, validation studies were carried out with the examples in the literature. As a result of each type of analysis giving consistent results, the effect of parameters on static buckling load was examined, while linear eigenvalue analysis method was used because it was also sufficient for cheaper analysis method and comparison studies. While displacementcontrolled analyses were carried out in the static buckling analyses mentioned, loadcontrolled analyses were performed in the analyses for the determination of dynamic buckling force. As a result of these analyses, they were evaluated according to different dynamic buckling criteria. There are some of the dynamic buckling criteria; Volmir criterion, BudianskyRoth criterion, HoffBruce criterion, etc. When BudianskyRoth criterion is used, the first estimated buckling load is applied to the structure and displacement  time graph is drawn. If a major change in displacement is observed, it can be assumed that the structure is dynamically buckled. For HoffBruce criterion, the speed  displacement graph should be drawn. If this graph is not focused in a single area and is drawn in a scattered way, it is considered that the structure has moved to the unstable area. As in static buckling analyses, dynamic buckling analyses were primarily validated with a sample study in the literature. After the analysis methods, the numerical studies were carried out on the effect of some parameters on the buckling load. First, the effect of the stacking sequence of composite layers on the buckling load was examined. In this context, a comprehensive study was carried out, both from which layer has the greatest effect of changing the angle and which angle has the highest buckling load. In addition, the some angle combinations are obtained in accordance with the angle stacking rules found in the literature. For those stacking sequences, buckling forces are calculated with both finite element analyses and analytically. In addition, comparisons were made with different materials. Here, the buckling load is calculated both for cylinders with different masses of the same thickness and for cylinders with different thicknesses with the same mass. Here, the highest force value for cylinders with the same mass is obtained for a uniform composite. In addition, although the highest buckling force was obtained for steel material in the analysis of cylinders of the same thickness, when we look at the ratio of buckling load to mass, the highest value was obtained for composite material. In addition, the ratio of length to diameter and the effect of thickness were also examined. Here, as the length to diameter ratio increases, the buckling load decreases. As the thickness increases, the buckling load increases with the square of the thickness. In addition to the effect of the length to diameter ratio and the effect of thickness, the loading time and the shape of the loading profile are also known in dynamic buckling analysis. In addition, the critical buckling force is affected by imperfections in the structure, which usually occur during the production of the structure. How sensitive the structures are to the imperfection may vary depending on the different parameters. The imperfection can be divided into three different groups as geometric, material and loading. Cylinders under axial load are particularly affected by geometric imperfection. The geometric imperfection can be defined as how far the structure is from a perfect cylindrical structure. It is possible to determine the specified amount of deviation by different measurement methods. Although it is not possible to measure the amount of imperfection for all structures, an idea can be gained about how much imperfection is expected from the studies found in the literature. Both the change in the buckling load on the measured cylinders and the imperfection effect of the buckling load can be measured by adding the measured amount of imperfection to the buckling load calculations. In cases where the amount of imperfection cannot be measured, the finite element can be included in the analysis model as an eigenvector imperfection obtained from linear buckling analysis and the critical buckling load can be calculated for the imperfect structure using nonlinear analysis methods. In this study, studies were carried out on how imperfection sensitivity changes under both static and dynamic loading with different parameters. These parameters are the the lengthtodiameter ratio, the effect of the stacking sequence of the composite layers and the added imperfection shape. The most important result obtained in the study on imperfection sensitivity is that the effect of the imperfection on the buckling load is quite high. Even geometric imperfection equal to thickness can cause the buckling load to drop by up to half.

ÖgeA study on optimization of a wing with fuel sloshing effects(Graduate School, 20220124) Vergün, Tolga ; Doğan, Vedat Ziya ; 511181206 ; Aeronautics and Astronautics Engineering ; Uçak ve Uzay MühendisliğiIn general, sloshing is defined as a phenomenon that corresponds to the free surface elevation in multiphase flows. It is a movement of liquid inside another object. Sloshing has been studied for centuries. The earliest work [48] was carried out in the literature by Euler in 1761 [17]. Lamb [32] theoretically examined sloshing in 1879. Especially with the development of technology, it has become more important. It appears in many different fields such as aviation, automotive, naval, etc. In the aviation industry, it is considered in fuel tanks. Since outcomes of sloshing may cause instability or damage to the structure, it is one of the concerns about aircraft design. To prevent its adverse effect, one of the most popular solutions is adding baffles into the fuel tank. Still, this solution also comes with a disadvantage: an increase in weight. To minimize the effects of added weight, designers optimize the structure by changing its shape, thickness, material, etc. In this study, a NACA 4412 airfoilshaped composite wing is used and optimized in terms of safety factor and weight. To do so, an initial composite layup is determined from current designs and advice from literature. When the design of the initial system is completed, the system is imported into a transient solver in the Ansys Workbench environment to perform numerical analysis on the time domain. To achieve more realistic cases, the wing with different fuel tank fill levels (25%, 50%, and 75%) is exposed to aerodynamic loads while the aircraft is rolling, yawing, and dutch rolling. The aircraft is assumed to fly with a constant speed of 60 m/s (~120 knots) to apply aerodynamic loads. Resultant force for 60 m/s airspeed is applied onto the wing surface by 1Way FluidStructure Interaction (1Way FSI) as a distributed pressure. Using this method, only fluid loads are transferred to the structural system, and the effect of wing deformation on the fluid flow field is neglected. Once gravity effects and aerodynamic loads are applied to the wing structure, displacement is defined as the wing is moving 20 deg/s for 3 seconds for all types of movements. On the other hand, fluid properties are described in the Ansys Fluent environment. Fluent defines the fuel level, fluid properties, computational fluid dynamics (CFD) solver, etc. Once both structural and fluid systems are ready, system coupling can perform 2Way FluidStructure Interaction (2Way FSI). Using this method, fluid loads and structural deformations are transferred simultaneously at each step. In this method, the structural system transfers displacement to the fluid system while the fluid system transfers pressure to the structural system. After nine analyses, the critical case is determined regarding the safety factor. Critical case, in which system has the lowest minimum safety factor, is found as 75% filled fuel tank while aircraft dutch rolling. After the determination of the critical case, the optimization process is started. During the optimization process, 1Way FSI is used since the computational cost of the 2Way FSI method is approximately 35 times that of 1Way FSI. However, taking less time should not be enough to accept 1Way FSI as a solution method; the deviation of two methods with each other is also investigated. After this investigation, it was found that the variation between the two methods is about 1% in terms of safety factors for our problem. In the light of this information, 1Way FSI is preferred to apply both sloshing and aerodynamic loads onto the structure to reduce computational time. After method selection, thickness optimization is started. Ansys Workbench creates a design of experiments (DOE) to examine response surface points. Latin Hypercube Sampling Design (LHSD) is preferred as a DOE method since it generates noncollapsing and spacefilling points to create a better response surface. After creating the initial response surface using Genetic Aggregation, the optimization process is started using the MultiObjective Genetic Algorithm (MOGA). Then, optimum values are verified by analyzing the optimum results in Ansys Workbench. When the optimum results are verified, it is realized that there is a notable deviation in results between optimized and verified results. To minimize the variation, refinement points are added to the response surface. This process is kept going until variation comes under 1%. After finding the optimum results, it is noticed that its precision is too high to maintain manufacturability so that it is rounded into 1% of a millimeter. In the end, final thickness values are verified. As a result, optimum values are found. It is found that weight is decreased from 100.64 kg to 94.35 kg, which means a 6.3% gain in terms of weight, while the minimum safety factor of the system is only reduced from 1.56 to 1.54. At the end of the study, it is concluded that a 6.3% reduction in weight would reflect energy saving.

ÖgeFonksiyonel derecelendirilmiş malzemeden üretilen plakların mekanik ve ısıl yükler altındaki burkulma analizi(Lisansüstü Eğitim Enstitüsü, 20220127) Aktaş, İbrahim Utku ; Doğan, Vedat Ziya ; 511171115 ; Uçak ve Uzay MühendisliğiMalzeme seçimi bütün mühendislik uygulamalarında çok önemli rol oynamaktadır. Neredeyse bütün mühendislik uygulamalarının gelişmesi ve ilerlemesi o alanda kullanılan malzemelerin gelişmişliği ile doğrudan ilişkilidir. Malzemelerin monolitik malzemeden alaşımlı malzemelere evrimi ve kompozit malzemelerin gelişimi, bir malzeme sınıfının çağın ihtiyaçlarına artık cevap veremiyor oluşundan doğmuştur. Çoğu mühendislik uygulamasında, monolitik bir malzemede bulunması imkânsız olan birbirleriyle çelişen özelliklere sahip malzemelerin kullanımına ihtiyaç duyulmaktadır. Ayrıca, farklı malzemelerin alaşımlanması, bileşen malzemelerin termodinamik davranışı ve bir malzemenin diğer malzemelerle karıştırılma derecesindeki kıstaslar ile sınırlıdır. Fonksiyonel derecelendirilmiş malzeme, iki malzemenin bir araya getirilmesi ve zorlu çalışma ortamlarına maruz kaldıktan sonra dahi işlevlerini yerine getirebilmesi ve özelliklerini koruyabilmesi gerekliliğinden doğmuştur. İşlevsel olarak derecelendirilmiş malzeme başlangıçta bir ısıl bariyer uygulaması ihtiyacı için geliştirilmiş olsa da, bu önemli gelişmiş malzemenin uygulaması artırılmış ve aşırı aşınma direnci ve korozyon direnci uygulamaları gibi mühendislik uygulamalarında bir dizi sorunu çözmek için kullanılmıştır. Bu yeni malzeme türünden havacılık, otomobil ve biyomedikal gibi uygulamalarda yararlanılmaktadır. Fonksiyonel derecelendirilmiş malzemeler, geleneksel kompozit malzemelerin zorlu çalışma ortamlarında kullanıldığında başarısız uygulamalara neden olmasının sonucunda ortaya çıkmıştır. Geleneksel kompozit malzemelerin mühendislik uygulamalarındaki başarısızlığı kompozit malzemeyi oluşturan katmanlar arasındaki belirgin bir şekilde tanımlanmış olan arayüzden kaynaklanmaktadır. Arayüz, bu bölgede yüksek bir gerilme yığılmasına sebebiyet vermekte ve kompozitin nihai başarısızlığına neden olan çatlak başlangıcını ve yayılmasını teşvik etmektedir. Bu çatlak oluşma ve ilerleme sürecine "delaminasyon" adı verilmektedir. Japonya' da bir uzay mekiği projesinde karşılaşılan ve fonksiyonel derecelendirilmiş malzemelerin ortaya çıkmasına ortam hazırlayan sorun, geleneksel kompozit malzemelerdeki bu belirgin arayüzün nasıl ortadan kaldırılabileceğini ve kompozitin istenen ısıl bariyer görevini nasıl yerine getirebileceği problemini ortaya koymuştur. Araştırmacılar, kademeli olarak değişen bir arayüz ile geleneksel kompozit malzemedeki keskin arayüzü sistematik olarak ortadan kaldırabildiler, böylece bu arayüzdeki gerilme yığılmasını azalttılar ve geliştirilen fonksiyonel derecelendirilmiş malzeme, zorlu çalışma koşullarında kırıma uğramadan ayakta kalabildi. Sonuç olarak malzemenin asıl geliştirilme amacı olan yapıya ısıl kalkan olması dışında çeşitli mühendislik uygulamaları için de fonksiyonel derecelendirilmiş malzemeler kullanılmıştır. Fonksiyonel derecelendirilmiş malzemeler, malzemenin hacmi boyunca değişen özelliklerle birlikte değişen bileşime sahip gelişmiş kompozit malzemelerdir. Havacılıkta kullanılan araçlar başta aerodinamik yükler olmak üzere birçok mekanik ve ısıl yüklere maruz kalmaktadır. Bu yükler hava aracının yapısallarının boyutlandırılmasında kullanılmaktadır. Güvenli bir hava aracı maruz kaldığı yükleri yapı içerisinde taşırken kırıma uğramayacak şekilde tasarlanmaktadır. Hava aracının yapısalları birçok farklı şekilde kırıma ya da hasara uğrayabilmektedir. Bunları öngörebilmek ve yapıyı ona göre tasarlamak hayati öneme sahiptir. Bununla beraber, yapıları kırıma uğratmayan fakat yapılarda yapısal kararsızlığa yol açan burkulma problemi havacılıkta çok önemli bir konudur. Örneğin bir uçağa gelen yükler kanat üzerindeki kabukların düzlem içi basma ya da çekme yüklerine maruz kalmasına sebep olabilmektedir. Kabuk elemanlarının basma yüküne maruz kaldığı durumlarda burkulma olayı gerçekleşebilir. Bu da hem kanat üzerindeki aerodinamik akışı bozabilmekte hem de yapının kararsız hale gelmesine sebep olabilmektedir. Bu gibi durumlarda yapının yük taşıma kapasitesi değişmekte ve burkulma sonrası hesaplamaların yapılması gerekmektedir. Bundan dolayı yapısal elemanların ne zaman burkulmaya uğrayabileceğini öngörebilmek büyük önem taşımaktadır. Bu tezde fonksiyonel derecelendirilmiş malzemeden üretilen plakların ısıl ve mekanik yüklemeler altındaki burkulma davranışları sistematik olarak ele alınacaktır. 1. Kısım' da yapılan çalışmadan genel olarak bahsedilip çalışmanın amacından ve isteğinden söz edilmiştir. 2. Kısım' da ise geçmişte fonksiyonel derecelendirilmiş plaklar üzerine yapılmış çalışmalar okuyucuya aktarılmıştır. Bu çalışmaları ifade etmeden önce temel burkulma probleminin tanımı yapılmıştır. Burkulma olayını tanımlamaya ilk olarak kolon ve kiriş elemanlarının burkulmasından başlanmış daha sonra plakların burkulması anlatılmıştır. Burkulma teorisinin alt yapısının okuyucuya bu şekilde verilmesi amaçlanmıştır. Ardından fonksiyonel derecelendirilmiş malzemelere kısa bir giriş yapılmış ve tarihçesinden bahsedilmiştir. Bu kısımda aynı zamanda fonksiyonel derecelendirilmiş malzemelerin burkulması üzerine yapılan akademik çalışmalardan da bahsedilmiştir. 3. Kısım' da fonksiyonel derecelendirilmiş malzemeden üretilen plakların mekaniğini anlamak adına geleneksel kompozit malzemeden üretilen plakların mekaniği okuyucuya aktarılmıştır. İlk olarak katmanlı kompozit plak teorilerinden kısaca bahsedilmiş ve sonra Klasik Kompozit Plaka Teorisi (KPT) ve Birinci Dereceden Kayma Şekil Değiştirme Teorisi (BKT) detaylı bir şekilde anlatılmıştır. Çünkü fonksiyonel derecelendirilmiş malzemeden üretilen plakların mekaniğini anlamak için geleneksel kompozit plakların mekaniğini iyice anlamak büyük önem taşımaktadır. 4. Kısım' da fonksiyonel derecelendirilmiş malzemelerin üretim yöntemlerinden kısaca bahsedilmiş ve etkin malzeme özelliklerinin nasıl modellendiği gösterilmiştir. 5. Kısım' a gelindiğinde daha önceden kısaca bahsedilen plakların burkulma problemi üzerinde durulmuş ve bu problemin belirli sınır koşulları altında analitik çözüm yöntemlerinden bahsedilmiştir. İlk olarak izotropik plakların burkulma probleminin çözümü, Navier ve Levy sınır koşullarını ayrı ayrı sağlayacak şekilde oluşturulan sınır koşulları altında çözülmüştür. Ardından Fonksiyonel derecelendirilmiş malzemeden üretilen plakların burkulma problemini çözebilmek için KPT kullanılarak analitik model oluşturulmuştur. Sonrasında oluşturulan analitik model her bir kenarından basit mesnetli kabul edilen fonksiyonel derecelendirilmiş plaklar için farklı yüklemeler altında MATLAB programında yazılan kod yardımı ile çözülmüştür. Bu yüklemeler mekanik ve ısıl yüklemeler olmak üzere ikiye ayrılmaktadır. Mekanik yüklemeler için üç farklı durum göz önüne alınmıştır. Bunlar: tek eksenli basma yükü, iki eksenli basma yükü ve iki eksenli basma – çekme yükü altındaki burkulma analizleridir. Isıl yükleme koşulları ise sıcaklığın kalınlık boyunca farklı şekillerde dağılımları göz önüne alınarak yine üç farklı şekilde yapıya uygulanacak ve burkulma analizi yapılmıştır. İlk olarak kalınlık boyunca sabit sıcaklık dağılımı için kritik burkulma sıcaklık farkı bulunmuştur. Ardından kalınlık boyunca doğrusal değişen sıcaklık dağılımı için burkulma analizi yapılıp kritik burkulma sıcaklık farkı elde edilmiş ve sonrasında ise kalınlık boyunca doğrusal olmayan sıcaklık dağılımı için bu analizler tekrarlanmıştır. Elde edilen tüm sonuçlar daha önceki çalışmalarla kıyaslanmış ve ince FD plaklar için KPT' nin oldukça başarılı sonuçlar verdiği görülmüştür. 6. Kısım' da ise sonlu elemanlar paket programı, PATRAN, NASTRAN yardımıyla burkulma analizleri gerçekleştirilmiş ve KPT ile elde edilen analitik sonuçlarla kıyaslanmıştır. Sonraki kısımlarda yapılan tüm çalışmalar kısaca değerlendirilmiş ve gelecekte bu konu üzerine yapılabilecek çalışmalardan bahsedilmiştir.

ÖgeModel predictive control based cooperative pursuit evasion for uav(Graduate School, 20220218) Akbıyık, Mustafa Berkay ; Acar, Hayri ; Özkol, İbrahim ; 511181131 ; Aeronautical and Astronautical EngineeringThis thesis proposes game theoretically model predictive control based guidance approach for pursuitevasion problem of uav's. The main idea is that guided swarm uavs pursue towards to adversary uav which evade to survive as long as possible. Game theoretical approach of pursuitevasion is based on designing the cost functions for each pursuer to converge adversary evader. Proposed approach is examined as decentralized. Therefore, each pursuer can be able to handle its mission independently without being affected by the other pursuer. The main contribution is the formulation of swarm pursuitevasion problem as the game theoretical which can enable to develop optimizationbased algorithms that bring superior strategies to pursuers for onetoone, twotoone scenarios during the air combat. This work proposes an algorithm to enhance applicability of the game theoretic nonconvex model predictive control problems on realsystems that have nonlinear controland state constraints. Proposed algorithm provide a model predictive controlbased guidance system which orientates the pursuers according to the evaders dynamics and positions. Nonlinear constraints are convexified along the finitehorizon time without loss of generality in successive linearizations. After discretization of dynamics, the suboptimal convex problem can be applied in model predictive concept for timecritical scenarios such as collaborative pursuitevasion of aerial vehicles.

ÖgeFlight safety risk awareness at flight test activities with analytical hierarchy process method(Graduate School, 20220523) Akgür, Yusuf ; Kodal, Ali ; 511191143 ; Aeronautics and Astronautics EngineeringIn 1903, the Wright brothers succeeded in flying the first manned and propelled heavierthanair aircraft, which soon led to the birth of aviation and the spread of aircrafts. Aircrafts, which started to be produced for different purposes, have caused many accidents and even deaths in their postproduction use and especially in the design development stages. Over the years, various arrangements have been made, international agreements have been signed, and local and international organizations have been established in order to prevent these accidents and deaths and to manage aircraft operations safely. Annex19 Safety Management System (SMS), which is the 19th and last annex of the International Civil Aviation Organisation (ICAO) Air Transport rules, is a system for managing the safety risks of organizations carrying out aviation activities and ensuring the effectiveness of safety risk controls, and includes systematic procedures, practices and policies for the management of these risks. Implementation of SMS in organizations carrying out civil aviation activities has started to be made compulsory by relevant local and international authorities. The studies which aim to prove whether the designed and manufactured aircraft provide the desired performance are called flight tests. Advances in technology, when incorporated into aircraft design processes, have led to the creation of formal requirements and specifications that provide universal benchmarks in aircraft design processes. Parallel to these developments, the aims and applications of flight testing have also matured and become a discipline. Flight tests are highrisk flights since they are carried out with aircraft that have not been certified yet, have low flight hours, and have many unknowns about the nature of the aircraft. For these reasons, within the scope of flight test activities, the risks should be determined in advance, necessary mitigation studies should be carried out and test procedures should be determined. It is stated in the Flight Test Operational Manuel (FTOM) guide document published by EASA that flight test organizations should improve the SMS. In this document, flight test risk management activities and risk management activities that must be carried out within the scope of SMS are separated. Flight test risk management was held responsible for the management of specific risks specific to each flight test, while SMS risk management was held responsible for operational risks that constitute continuity. Within the scope of this study, the Analytical Hierarchy Process (AHP) method, which is a hierarchical weighted multipurpose decision analysis method that combines qualitative and quantitative analysis methods, was used to provide a holistic awareness of flight safety risks in flight test activities. When using the weighting function of the AHP method, the safety risk matrix published by the SMS risk management of the relevant institution is based on and it is aimed to determine how important the risks are to each other. The values selected from the risk matrix for the risk specific to the flight test and operational risks are multiplied with the coefficients to be determined for each risk level to create a comparison matrix and the weight of each risk is calculated. It is expected that the flight test risk will have the largest share in the weighting to be achieved, and the evaluation of the results in this direction. Providing corrective feedback on the coefficients determined for each risk level, the choice of risk value and the structure of the risk matrix are the gains that can be achieved in addition to flight safety risk awareness. The use of the safety risk matrix and the values here while calculating the weights of the risks eliminates the subjective evaluation in the AHP method and makes the consistency index 0. However, the method used is subjective due to the structure of the risk matrix, the selected risk values and coefficients. For this reason, the returns to be obtained in line with the outputs of the method will allow these subjective values to change and take their optimum form over time. This study, which started in line with the definitions in the EASA Part21 FTOM Guide document, became an example of how Flight Test Risk Management and Safety Management System can work together. As a result, it is aimed to raise awareness of the flight safety risks involved in Flight Test Activities to the relevant flight test team by making use of the weighting feature of the AHP method.

ÖgeKademeli ve düz kiriş yapılarının termal etki altındaki titreşim davranışının incelenmesi(Lisansüstü Eğitim Enstitüsü, 20221015) Altıntaş, Furkan ; Kaya, Metin Orhan ; 511181118 ; Uçak ve Uzay MühendisliğiKiriş yapılarının başta havacılık olmak üzere otomotiv ve inşaat sektöründe oldukça yaygın bir kullanım alanı vardır. Genel olarak, boyuna ve enine dik yükleri destekleyen kiriş yapılarının uzunluğu kesit ölçülerine göre oldukça büyüktür. Kirişler, eksenine dik olan yükleri taşır ve bu nedenle yükler uzunluğa dik doğrultudadır. Kullanım alanı oldukça geniş olan kiriş yapılarının analizinde çeşitli metotlar ve teoriler bulunmaktadır. Bu çalışma kapsamında EulerBernoulli ve Timoshenko kiriş teorileri incelenmiş, kirişlerin titreşim davranışının incelenmesi amacıyla titreşim denklemleri elde edilmiştir. Bir dizi diferansiyel denklemden oluşan titreşim denklemlerinin çözümü için oldukça yaygın ve pratik çözüm yöntemi olan Diferansiyel Dönüşüm Metodu (DDM) kullanılmış, sonuçlar analitik çözüm ile kıyaslanmıştır. Diferansiyel Dönüşüm Metodu için MATLAB kodu oluşturulmuş, çözümler geliştirilen kod yardımıyla elde edilmiştir. Bu teorilerin haricinde günümüzde kullanımı yaygınlaşan Sonlu Elemanlar Yöntemi(SEY) ile de sonuçlar elde edilmiş ve analitik sonuçlar ile karşılaştırma yapılmıştır. Sonlu Elemanlar Yöntemi'nde ABAQUS paket programı kullanılmış, kiriş modellemeleri bu yazılım ile yapılmıştır.Uçak yapıları yüksek mukavemete ve yorulma dayanıma sahip oldukça hafif yapılardan oluşmaktadır. Bu bağlamda tez çalışmasında incelenmek üzere kiriş yapı malzemeleri olarak çeşitli metalik ve kompozit malzemeler belirlenmiştir. Kompozit malzemelerin elastik karakteristikleri belirlenmesi için kompozit teorisi kullanılarak laminaların mikromekanik ve makromekanik analizi yapılmıştır.Sıcaklıkla ilgili fenomenlerin yapılar üzerindeki etkisi oldukça geniş bir çalışma alanına sahiptir. Sıcaklıktaki değişiklik, kirişin titreşim davranışında büyük bir değişikliğe sebep olabilir. Bu tür yapıların dinamik davranışları yapının termal genleşmesine ve malzeme özelliklerine bağlı olarak sıcaklık etkisiyle değişmektedir.Bu tez çalışmasında sıcaklık değişiminin kirişlerin davranışına etkisini incelemek amacıyla elde edilen titreşim denklemine sıcaklık terimi eklenmiş ve çözümler yinelenmiştir. Belirlenen beş farklı sıcaklık değişimi için sonuçlar karşılaştırmalı olarak verilmiştir. Kesiti, uzunluğu boyunca değişken olan kirişlere kademeli kirişler denmektedir. Uçaklarda kullanılan kanat yapılarını ele aldığımızda, uçak gövdesinden uzaklaşıldıkça kanat kesiti küçülmekte dolayısı ile kesit değişmektedir. Bu yapılar da çalışma kapsamına dahil edilmiş, düz kirişlere ek olarak kademeli kirişler de incelenmiştir. İncelenmek amacıyla uzunluğu boyunca farklı oranlarda kesiti ve malzemesi değişen çeşitli kirişler oluşturulmuş, titreşim denklemleri elde edilmiştir. Düz kirişler, ankastre mesnetserbest uç, ankastre mesnetankastre mesnet, ankastre mesnetkayar mesnet ve sabit mesnetkayar mesnet olmak üzere dört farklı sınır şartında incelenirken kademeli kirişler ise ankastre mesnetankastre mesnet sınır şartında incelenmiştir. Sonuç bölümü oldukça detaylı oluşturulmuştur. Her bir malzeme ve kesit için beş farklı sıcaklık değişimi için sonuçlar EulerBernoulli, Timoshenko kiriş teorisi ve SEY çözümü yapılarak tablolar ile verilmiştir. Sıcaklık etkisinin kirişin titreşim davranışına etkisinin ve farklı sınır şartlarının incelenmesi ile diğer çalışmalar için temel oluşturması amaçlanmıştır.

ÖgeAnalysis of aircraft landing gear brake induced vibrations(Graduate School, 20230123) Altınbağ, Öner ; Balkan, Demet ; 511191131 ; Aeronautics and Astronautics EngineeringToday, aviation systems are the product of more than 100 years of work. The most groundbreaking process in these studies was experienced during the cold war years. The achievements of many engineering activities today are based on the knowledge gained in these years. Some major problems have been completely resolved in this progress, and some of them still continue to be active problems. The landing gear system is always critical to aircraft and is the engineering solution for almost all functions on the ground. In recent years engineers have been trying to optimize previous achievements within the framework of weight reduction, reliability, integration, energy consumption, noise reduction, cost reduction, and maintenance activities. One of the most important problems related to landing gear systems from the past to the present is the vibration problem, which we can examine under noise reduction. In this study, the causes of vibrations originating from the landing gear braking system were examined together with previous studies in the literature. A comparative approach to brakeinduced vibrations, which is still seen as a problem today, has been sought as a solution using today's tools. In this context, the parameters required for an aircraft landing gear model were calculated with the preliminary design activities used in the literature and industry. With these calculations, a model was created using MSC ADAMS software. Tire models in multibody dynamics simulations for vehicle dynamics were examined. As a result, the most suitable tire model was selected for the scope of the study. The parameters of the relevant tire model have been modified from the result of the tire sizing calculations. Two different vibration frequencies were investigated under four different longitudinal velocity conditions in order to make a valuable comparison. The results obtained from the model were compared and interpreted by using the previous studies from the literature.

ÖgeDatadriven delay estimation and anomaly detection: A study on European and Turkish air traffic(Graduate School, 20230518) Aksoy, Muhammet ; Koyuncu, Emre ; 511201136 ; Aeronautical and Astronautical EngineeringAir traffic networks represent highly complex and interconnected physical systems. Unlike other transportation networks, air traffic is very heavily regulated and physically constrained. Although the airways and airspaces are somehow more flexible compared to land based transportation systems, the fact that aircrafts can only positioned on and operated by airports make them quite dependent on the operations of the airports. Air traffic is regulated to ensure safety, while also maintaining the throughput of travel from one location to another. While these regulations does a decent job on keeping the air travel safe and systematical, they fall short when there are disruptions among the network that hinders the air traffic. There are numerous reasons for disruptions in air transportation; weather conditions, accidents, capacity constraints, personnel strikes etc. Yet their negative effect to the air traffic is mostly the same: introducing delays. Due to the connected nature of the air traffic and airports, when a delay generating event occurs at one place, the other members of the network could experience the similar effects, if not at a larger degree. This delay propagation means there is a ripple effect through the network which can snowball the delay generations and cause very large congestions. To relieve the effects of delay generating events, air traffic federators regulate the air traffic in a reactionary way. This may include reducing the capacity on certain airports or airways, giving NOTAMs, holding aircrafts on the ground or in the air (with hold patterns). Since all these actions are \emph{reactionary}, they are set in place after the delays already propagates through the network since it is trivial to asses and quantify the propagations in a large and complex network system. This study hypothesis that if the air traffic network can be modeled so that the propagations can be accurately calculated, it becomes possible to take proactive actions instead of reactive ones. Proactive actions are significantly more important when there is a risk of snowballing and propagation. It allows to take action when the ill effects are still contained on fewer members with smaller intensities. This paves the way for a more effective and less costly approach. Hence, the study proposes a method with 3 main parts; first one is to model the air traffic network so that propagations can be quantified, second one is to estimate the parameters of this model to keep a shortsighted vision into the upcoming network state and third one is to come up with a comprehensive action generating model to find optimal proactive actions that can keep the delay spreading at minimum and improve system resiliency. The air traffic modeling part is done via adopting compartmental model from epidemiology. This model explains the tranmission of disease within a population. When it is applied to the physical network system, instead of disease and humans, the delay amount and aircrafts is used. Additionally with the meta population model, instead of considering aircrafts one by one, airports can be used as they are focused points of aircraft populations. By linking transmit rate to the flight frequency between airports and the recovery rate to the delay handling characteristics of the airport, The parameter estimation part is done by calculating the historic recovery rates of the airports and then using deep learning inference to predict the next time step's recovery rates. The other parameters of the air traffic model, such as the traffic flow, is already known before hand (flight plans). Therefore through the estimation of recovery rate the network state of the upcoming states can be accurately predicted. This prediction can then be fed to the action generating algorithm to make the most informed decision. The action generating algorithm therefore must fundamentally be a deterministic state to action mapper. Reinforcement learning approach is utilized to train this state to action mapper to make it capable of generating optimal decisions under a sufficiently large spectrum of conditions. The final part of this study concerns with anomalous flight detection in air traffic as these types of flights are one of the sources of disruptions in an air traffic network. Although flight paths naturally diverge from one another, they still adhere to a set of patterns that have been tested in various environments and are optimized for them. These patterns may or may not be simple, depending on a number of factors, such as airspace use, the cognitive complexity of controllers, the weather, and NOTAMs. It is a challenging task to accurately classify flights just by their trajectories into a desired set of categories based solely on its statistical properties because of the high variance. For this purpose, the study incorporates a statistical approach that takes into account the timebased characteristics of the flight trajectories to determine whether they are abnormal or not. This statistical method with LSTM autoencoders makes it possible to train the model with historical data and quickly predict the flight class, taking into account the timebased characteristics of a flight trajectory. LSTM autoencoders can capture the class of a flight with relatively shorter time windows (16 second intervals). Therefore the air space can be periodically sweeped for anomalies while the network model and action algorithm runs in parallel. The obtained results demonstrate that the suggested architecture is quite capable of classifying abnormal flight trajectories as it successfully detects simulated fighter aircraft trajectories in airspaces with high commercial flight density. With the applications of deep learning and reinforcement learning, this whole methodology ensembles is largely datadriven, however the introduction of the compartmental model from epidemiology lays out a strong and accurate mathematical formula to support these datacentric approach. As the results suggests, The whole network's resiliency, i.e. its ability to keep delays from spreading and absorbing them, significantly increases when the optimal actions are reflected on the parameters. Additionally with the help of unsupervised learning, anomalous flights are also detected and represented as a disruption source to the network. Possible biases and shortcomings due to the datadriven approach is recognized throughout the study yet the overall method is deemed to be of significant importance in terms of managing resiliency through air traffic networks.