LEE- Savunma Teknolojileri-Yüksek Lisans

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http://hdl.handle.net/11527/19451

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Laser induced graphene based flexible gas sensor for wearable electronics

(Lisansüstü Eğitim Enstitüsü, 2020-07-21) Büyükturgay, Mehmet Mert ; Solak, Nuri ; 514181008 ; Defence Technologies ; Savunma Teknolojileri

From the past to the present, the most important thing to consider when developing defense systems is the production of original technology. The industrial power of a country is dependent on its technology. In this sense, it is important for countries to improve their original technologies. Technology is also important in the means of the privacy, reliability, and foreign dependency of defense systems. Production and development of high technology defense systems open a country's way to the domination of the world market, hence increasing the living standards of its citizens. This situation causes competitiveness in the field and in order to establish military domination, it is essential for countries to be able to produce and improve high-technology defense systems. Electronic technologies are also important in the defense systems industry. Since electronic technologies are widely used, engineers usually spend more shift hours designing and developing these products. There are lots of parameters in order to make these products ideal to be used in the defense systems industry. It is important and necessary for defense systems to be smaller in size, lightweight, with less effort and power required, practical, and faster in data transmitting. However, it may not always be easy to meet these necessities. In designing a product, just meeting one of these necessities may require a million dollars. The widespread use of electronic technologies results in the formation of new systems that are smaller, lightweight, and microchip controlled. In a changing and developing world, software updates of defense systems are also very important to function effectively. At the same time, the textile industry has recently begun to shift from traditional textile products to intelligent new textiles that process information to meet the demands and requirements of the defense industry. This situation resulted in engineering fields such as material science, electronics, and chemistry leading the textile industry and in the formation of a new multidisciplinary working area. Sensors compose almost the entire range of the smart textile field and unlike traditional textiles, it is a field open to new technological developments. Smart textiles are usually designed and developed for military technologies and the health sector. Wearable technologies complete duties such as obtaining and processing important data from the environment and simultaneously sending and visualizing these data to different sources. Smart clothing developed for area scanning and search and rescue teams may provide life safety for both search and rescue and military staff. They may also make any intervention more effective. Furthermore, information such as hazardous toxic gasses, amount of oxygen, and temperature of the potential risk zone and accident area may be obtained through this technology. This information is sent to different sources simultaneously and necessary measures are taken immediately. With the development of this system, risk analysis may be carried out in more detail, based on the information obtained from risky regions. The smart sensors may also be used in the exploration of the risky area; hence making the planning and application of the required intervention safer. Gas sensors play a major role in war fields and accident areas. Nowadays many countries are producing various chemical and biological weapons, so it is a necessity for every country to develop its own defense systems and take necessary precautions. New smart gas sensors are being developed as protection systems in case of the usage of these weapons. Gas sensors are not only used in the field of military defense systems; they are also used in companies where chemicals are frequently used and in highly populated regions in order to protect the health of workers and individuals by distinguishing hazardous and non-hazardous gasses in the air. Today, although many types and functions of commercial products are produced, problems in detecting hazardous gasses have not been solved completely. The problems that usually vary according to the type of sensor and need to be solved are as follows; the size of the sensor may not be small enough, low sensitivity and selectivity, long response time, not being suitable for long-term use, easy abrasion, sensitivity to movement, measurement errors due to environmental factors, high energy consumption, and difficulties in production and high costs. Briefly, more advanced and smart devices are needed, in order to detect what type of gasses are in the air. In this study, different sensor technologies and systems were studied to detect toxic or hazardous gasses. A major part of this study consists of research that accounts for precision, selectivity, response intervals, flexibility, resistance, size, and portability of the sensors. Even in their applications in daily life, sensors should be able to obtain data while they are in motion and transmit this data to distant sources. Therefore, in order to prevent the limitation of motion, the sensors should be portable and flexible enough to wrap the body easily. Wearable sensors that are designed compatible with clothing are more effective and useful than handheld sensors. The aim of this study is to determine whether the environment is dangerous or not in terms of gas type and to ensure that this information is transmitted to the source. Since this study is designed in the means of wearable technology, the disadvantage of carrying any device is eliminated. In addition, with the help of the sensor and resistance meter on the clothing, instant toxic gas contact can be detected. Therefore, staff on duty are able to obtain data from the environment simultaneously and can act more precautious to the current situation. First, a 3D graphene sensor was produced on the polyimide PI film using laser direct writing to create direct ammonia gas sensors. At this stage, first, the CO2 laser to be used has been optimized, the focus of the laser has been determined and the optimum parameters that will affect the final product have been determined. Then, carbonization and graphitization processes were applied according to these parameters. However, the necessary software was previously installed on the CO2 laser to implement this phase. With the help of the "Inkspace" application, sensors are designed and drawn. Then, with the help of the "K40 Whisperer" driver, the previously drawn sensors were transferred to the memory of the laser. The laser system was controlled with this driver, the predetermined parameters were entered into the system and the laser engraving process was started. As a result of this process, the desired laser-induced graphene products were obtained. The bending test was applied to the graphene sensors obtained. The products that were successful in this test were tested again for resistance with the help of a digital multimeter. The samples obtained after these tests were used in the specially designed NH3 gas sensor system. After the LIG sensor specimens were obtained, the chamber was ready to be installed. NH3 gas sensor mainly consists of a bottle of ammonia gas (25%), a micro syringe, control switches, a jar for the gas mixing system, a jar for the chamber, 1 air fan, 2 pneumatic pipes (1 for gas inlet and 1 for gas outlet), a digital multi-meter and pre-produced graphene sensors. This test was done at room temperature and room atmosphere. First, a micro syringe was filled with a certain volume of NH3(25%); then it was injected into a gas mixing system. A certain concentration of ammonia gas(100ppm-1000ppm) was obtained by mixing with ambient air in the mixing system. After that, the first switch was turned on and the mixing gas vapor was transferred to the test chamber near the LIG sensor. The LIG specimen was placed inside the chamber. In this system, one of the control switches was used to transfer a certain concentration of ammonia gas to the chamber and the other switch was used to release the gas from the chamber. Thus, a certain concentration of ammonia gas was circulated in the chamber homogenously with the help of the air fan. The digital multimeter that was used in this chamber is able to show the resistance of the sensor when it was exposed to ammonia gas and the atmosphere. As a result of the changing ambient atmosphere, the resistance meter connected to the graphene sensor showed a resistance change due to NH3 gas contact. Therefore, ammonia gas sensing was carried out. As a result, a flexible graphene-based gas sensor was produced, which detects whether there is any ammonia gas as a warfare gas simulant in the atmosphere. The produced graphene-based gas sensors can operate at room temperature with high selectivity and low power consumption. Thus, this study can be an important candidate for today and future applications of wearable detectors in both military and many other fields.
Çok maksatlı savaş uçağı iniş takımlarında bağlantı elemanları tasarımı ve analizi

(Lisansüstü Eğitim Enstitüsü, 2022) Orhan, Oğuzhan ; Özkol, İbrahim ; 721591 ; Savunma Teknolojileri Ana Bilim Dalı

Bu tez çalışması kapsamında iniş takımlarının tarihsel süreçte gelişimi incelenerek, günümüz modern savaş uçaklarından Savaşan Şahin F-16 savaş uçağı iniş takımlarının gövdeye bağlantı elemanında(FS 341.8 Bulkhead) meydana gelen deformasyonun araştırılması, daha uygun malzeme ve tasarım seçeneklerinin geliştirilmesi ve en sonda optimum bulunan çözümün uygulanarak analizinin çeşitli şartlar ve farklı durumlarda uygulanması süreci araştırılmıştır. Uçaklar, temel olarak 5 ana bölmeden oluşmaktadır. Bunlar; uçakta yer alan tüm bölmeleri, dolaylı ya da doğrudan bağlandığı, görev tanımına göre yolcu, mühimmat ya da motoru içinde barındıran gövde yapısı, uçakların havada kalmasını, taşınmasını sağlayan kanat yapısı, uçağın dengeli bir uçuş gerçekleştirmesini sağlayan kuyruk yapısı, uçaklarda itiş gücünü sağlayan motor yapısı ve son olarak uçakların kalkış ve inişte üzerinde yol aldığı ve desteklendiği iniş takımı yapısıdır. İniş takımları, uçağın yerle olan bağlantısını sağlaması, inişte gerçekleşen yüksek kuvvet ve gerilmelerin absorbe edilmesi, sönümlenmesi, dengeli ve hasarsız bir inişin, kalkışın ve taksilemenin gerçekleşebilmesi için kullanıldığından uçak yapısında çok önemli bir yere sahiptir. Birçok görevi yerine getirmesi sebebiyle kompleks bir yapıya sahip olan iniş takımları uçağın tasarımı sürecine göre birçok mühendislik biliminin ortak çalışmasının sonucu olarak ortaya konmaktadır. Yapısal tasarım ve hidrolik mühendisliği, ağırlık ve aerodinamik hesaplamalar, pistle alakalı mühendislik incelemeleri ve ekonomik seçimler ve hesaplamalar düşünüldüğünde birçok farklı bilim dalını ve mühendislik alanlarını içerdiği gözlemlenmektedir. Tezde giriş bölümünde tüm tez yazım süresince yapılan araştırmalar, gözlemler ve uygulamalar hakkında temel bilgilendirme yapılmıştır. İşleyiş sıralamasına uygun biçimde tez aşamalarının bilgileri aktarılmıştır. İkinci bölüm kapsamında literatür araştırması yapılarak farklı görev tanımlamalarına göre değişik özelliklere ve fiziksel yapıya sahip iniş takımları üzerinden iniş takımlarının sahip olduğu komponentler hakkında bilgilendirme yapılmış, bu sistemlerin nasıl konumlandırıldığı birbirleriyle ilişkileri ifade edilmiştir. Uyum halinde çalışan sistemlerin işleyişleri ve özellikleri belirtilerek bu yapılara ait hesaplamalar ve gereklilikler anlatılmıştır. Literatür araştırmasından edinilen bilgilerle yeni nesil çok maksatlı savaş uçağı F-16 Savaşan Şahin'de(Fighting Falcon) kullanılan iniş takımlarının özellikleri üçüncü bölümde incelenerek, tasarım, gereksinimlere göre seçim ve uygulama hakkında detaylı çalışmalar gerçekleştirilmiş ve sunulmuştur. Bu bölümde boyutlandırma, görev, uçak ağırlığı ve hız parametreleri düşünülerek gerçekleştirilen sistem tasarımları incelenmiştir. Dördüncü bölümde gerçekleştirilen tasarımlarda ömür süresi uzatılmak istenen iniş takımının ana gövdesine bağlanma yapılarındaki deformasyonlar ortaya konularak problemlere getirilen çözümler anlatılmıştır. Savaş uçaklarının hızlarına ve ağırlıklarına bağlı, kısa mesafe iniş için gerekli olan frenlemeler sebebiyle olası tehlikeler ve yapılarda meydana gelen deformasyonlar ile ömür hesaplamaları gerçekleştirilmiştir. Son olarak gerçekleştirilen ölçümler sonucunda yapılarda gerçekleşen deformasyonu azaltıcı tasarım ve malzeme seçilimi hakkında yeni öneriler ve sonuçlar verilmiştir.
Fighter pilot behavior cloning and transferring to another aircraft

(Graduate School, 2022) Sever, Gülay ; Üre, Nazım Kemal ; 772812 ; Autonomous Systems Programme

he "Pilot-in-the-loop" flight simulators are important tools in the development of fighter aircraft because they allow engineers and designers to test different scenarios and algorithms in a controlled environment without the risks associated with actual flight testing. However, these simulations often require high pilot skill levels and can be time-consuming and costly to arrange. It is important to create realistic models of human fighter pilots in order to reduce the reliance on skilled pilots to demonstrate agile/aerobatic maneuvers in flight simulators. Traditional controllers for aircraft require detailed knowledge about the aerodynamic model and physics of the aircraft in order to perform aerobatic maneuvers. Also, these control algorithms may not be able to match the performance of skilled human pilots, who are limited by a lack of bandwidth. This suggests that there may be potential for improving the performance of aircraft through the use of techniques that can take advantage of the superior speed and maneuverability of skilled pilots. In that case, imitation learning is a potential solution to eliminate the dependency need of skillful pilots in the flight simulator. Imitation learning also known as learning from demonstrations has benefited from computational progresses brought on by deep learning and increased availability of demonstration data. It is aimed to emulate desired behavior in a given task. An agent is trained to learn mapping between observations and actions by utilizing demonstrations. In this thesis aims the development of a pilot behavior model which is capable of autonomously performing agile maneuvers and is able to replace expert pilots' demonstrations over its full flight envelope in the flight simulator. Moreover, this model is transferable to other aircraft with limited data using transfer learning techniques. Besides all these features, the pilot behavior model can be able to run in real time in the flight simulator.
Aircraft trajectory optimization under wind effect by using optimal control : Environmental impact assessment

(Graduate School, 2022) Sezenoğlu, Fulin ; Özkol, İbrahim ; Defence Technologies Programme

The aim of this thesis, Aircraft Trajectory Optimization Under Wind by Using Optimal Control and Environmental Impact of Aviation in terms of Aircraft Emissions, is to find the wind and weather optimized aircraft trajectories in the cruise phase by minimizing fuel consumption, time and air pollutants. Flight trajectories calculated by taking into account the wind factor are considered as a critical measure in terms of reducing fuel consumption. In addition, it is known that the models examined by including weather information give more realistic results than those that are not included. Trajectory planning calculations consist of various elements such as wind forecasts, operational constraints, amount of fuel, aircraft performance, atmospheric conditions. Temperature, pressure and air density parameters are considered standard atmospheric values. The performance model used is based on BADA. In order to achieve the aims of the thesis, first of all, the problem has been tried in 2 dimensions in terms of reducing complexity of operations. At this stage, the wind equation, which was created with a simple calculation, was added to the EoM in horizontal plane. The effect of the horizontal components of wind is clearly seen in the numerical simulation. Secondly, the problem was created according to BADA 3 and solved in a way that minimizes flight time and fuel in 3 dimensional space. Simultaneously, a wind model has been created with the wind tabular data obtained from the Global Forecast System (GFS). The GFS is a weather forecast model developed by the National Centers for Environmental Prediction (NCEP). In this study, wind factor was assumed to be stationary, wind uncertainty was not included in this study. Since there are erroneous measurements in the wind tabular data obtained from the Global Forecasting System (GFS), the data was improved by applying the interpolation method first and the error difference between the real data and the interpolated data was arranged to be the least. Then, with the smooth data, wind equations were obtained separately for seven barometric altitude levels. Thirdly, in addition to flight time and fuel consumption, an emission model was created based on the ICAO Engine Exhaust Data Bank [29] and Boeing Method 2 [30] to solve the multi-objective optimization problem. The developed new model was applied to the simulation environment created based on BADA 4. Finally, the wind equations in the horizontal plane obtained were included in the simulation environment developed on the basis of BADA 4, and the targeted model was created. Predetermined routes were filtered from the actual flight plan selected for the same day with the wind data to be examined in the case studies. The flight area was determined and a wind model was obtained for that region. All one-day flights for the selected route were examined. Wind equations are calculated by taking flight hours into account. The simulation results were obtained according to the flight information of the desired route obtained from the real flight plan. The optimized trajectories were calculated in the simulation environment by referring to the points where the aircraft started and ended the cruise phase. Thus, Turkish airspace, which has not been examined before, is presented as a case study specific to Istanbul-Ankara flights. As a second case study, European airspace is presented specific to Paris-Frankfurt flights. During these studies, it was clearly seen that cruising speed and cruising altitude are critical for fuel consumption under the wind effect. In addition, as a result of these studies, it has been shown that the proposed model gives more effective results as the flight distance increases. This study consists of five chapters describing the stages of the thesis. The first chapter is a general introduction to the thesis topic. The thesis topic is explained and its aims are mentioned, the importance of the subject and why it is needed are presented. This section consists of three sub-titles. First of all, the scope and contributions of the thesis are mentioned. Afterwards, a wide literature review was made and studies in this field were presented. Finally, the structure of the thesis is mentioned. In the second chapter, the mathematical model required for this study is explained. Wind-optimized trajectories for an aircraft in the cruise phase are generated by solving a non-linear optimal control problem. For this reason, first of all, the general representation of the optimal control problem and its solution techniques are mentioned. The suitability of these solution techniques to the problem is discussed and the method to solve the problem is explained. It is known that multi-objective optimization problems give more realistic and ideal results than single-objective optimization problems. After this part, multi-objective optimization problem and constraints are defined. In the last part, the optimal control problem solution method is mentioned. GEKKO Python optimization module was used for numerical simulation in solving the aircraft trajectory optimization problem. This algorithm was developed to analyze the environmental impact of emitted aircraft emissions such as nitrogen oxides and carbon dioxide, using real air traffic data. In the third chapter, models used in trajectory generation optimized for wind and weather conditions are introduced. First, the assumptions are mentioned. Afterwards, the atmosphere model, aircraft performance model, wind model and emission model are explained in detail. In addition, the equations of motion of the aircraft in 2D and 3D are shown in this section. In the fourth chapter, two case studies on the subject and their results are presented. First of all, it is the main contribution to the literature to analyze the flights over Turkey, which has not been focused on before as a case study. First, the problem is defined in the case analysis. Then, the wind field over the Turkish airspace was examined and a wind model was created. The wind equations of the region, which was extracted to include Istanbul and Ankara, were obtained and added to the equations of motion of an aircraft, as explained in wind model section in third chapter. In the simulation environment created in this direction, the most optimized trajectories were calculated considering the Istanbul-Ankara flights. As the second case study, Paris-Frankfurt flights over European airspace were analyzed. As in the first application, after defining the problem respectively and examining the wind field covering the flight points, the multi-objective optimization problem was solved for this route. As a result of the case studies, the actual and calculated flight time, fuel consumption, NOx and CO2 emission findings for each flight are presented comparatively. In the fifth and also the last chapter, the results and other studies that can be done in this field are mentioned. The values obtained as a result of the case analyzes are emphasized again. Within the scope of the study, it has been shown that the adverse impacts of aviation on the climate are reduced by trajectory optimization, which is resolved by evaluating wind and environmental effects. The topics that can be studied on the basis of this study in the future are mentioned.
Integrated vehicle control unit development with active safety functions for electric vehicles

(Graduate School, 2022) Ünver, Muhammet Mustafa ; Gökaşan, Metin ; 514181009 ; Defense Technologies Programme

The importance of electronic control systems has increased with the increase in safety standards for the driver and passengers on both the commercial and defense side in the automotive. In this thesis, the developed integrated vehicle control unit for military electric land vehicles is only one of dozens of electronic control units used on the vehicle. It is called an integrated system because of the functions of the different control units it contains. To list these functions, it consists of vehicle mode determination, torque demand from the accelerator pedal, power management system, motor torque limiting, regenerative brake control, fault detection and safety function, traction control and vehicle stability control subsystems. Traction control and vehicle stability systems are among the most complex functions of the integrated vehicle control unit. These complex systems are functions of active safety systems. Active safety systems come up with the names of ABS, TCS and ESC today, and they take control of the vehicle partially or completely by detecting any uncontrolled vehicle movement or condition that may occur while driving through the sensors or systems on the vehicle. In this way, it aims to prevent accidents by managing the vehicle in a more stable and controlled manner. Active safety systems have become a necessity in commercial vehicle applications as per the standards, and their use in military vehicle applications has become increasingly widespread in recent years. The main purpose of the TCS system is to automatically provide traction control by activating in case of loss of traction in any of the wheels due to road conditions such as wet or icy ground. With the use of the TCS system, the road holding and steering control that will decrease due to the loss of traction are prevented. It detects the wheel slip rate by reading the vehicle speed and wheel speed, and accordingly, it optimizes the torque demand from the driver and requests torque from the motor to keep the slip rate at the level where it can provide the most road grip compared to the road surface. The ESC system is an active safety system developed to keep the vehicle on the road in the desired direction, to intervene with the motor torque and the brakes independently of each other. It optimizes how much torque to the vehicle and to which wheel it will brake, by means of the information it reads from various sensors on the vehicle. In sharp cornering turns, depending on the steering ratio and vehicle speed, it tries to keep the vehicle on the road in the desired direction by making independent braking interventions to the wheels in order to prevent the vehicle from skidding. In order to perform simulation tests of the functions of the integrated vehicle control unit, an electric military land vehicle dynamic model has been developed within the scope of the thesis study. The developed model consists of steering unit, electric motor, battery, powertrain, brake fluids, wheel and vehicle body subsystems. As functions for vehicle dynamics have been developed on the control side, the wheel and vehicle model have been designed in more detail in the vehicle model. For example, the TCS system developed for the vehicle control unit uses the wheel and vehicle speed to calculate the longitudinal wheel slip rate. The wheel model was needed to calculate the wheel speed in the simulation tests. The wheel model was developed with the Pacejka Magic Formula approach as it is suitable for characterizing longitudinal and lateral behavior.
Aeroacoustic investigation of unsteady transonic cavity flow via open CFD source codes

(Graduate School, 2022-01-03) Fadıl, Ali Can ; Zafer, Baha ; 514191004 ; Defense Technologies

Cavity flow research has been ongoing since the 1940s, especially for weapon bay use in fighter aircraft. With the development of acoustic analogy by Lighthill, aeroacoustic studies have also embarked on cavity flow. The studies which were firstly done for military purposes have expanded intending to reduce the aerodynamically generated noise that may disturb the comfort of the passengers and the inhabitants near the airport. As time progresses, new regulations are made on this subject and the maximum decibel limit is gradually being lowered. Hence, it is aimed to prevent noise pollution, especially in big cities. As stated above, the cavity geometry examined within the scope of the thesis can be seen in the weapon bay of warplanes, the landing gear of warplanes and passenger planes, the door cavities, sunroofs and windshield openings of automobiles. Since these flow types contain more than one phenomenon in terms of fluid mechanics discipline and their modeling is relatively effortless, they represent a fundamental problem on which intensive studies have been carried out. Modern military warplanes and unmanned warplanes tend to carry their ammunition in weapon bay embedded in the fuselage, rather than wing, to reduce the radar cross-section as much as possible and to operate without being detected by the radar systems. Flow events that occur in the weapon bay during the ammunition separation of warplanes that carry bombs and missiles in their internal weapon bay may cause the bomb not to leave the aircraft in a safe and correct trajectory, resulting in undesirable consequences and hence it is of crucial importance to understand and analyze them. Although it looks geometrically simple, cavity flows have indeed complex structures due to the effects of high velocity, pressure, density gradients, turbulence, and instability. As a result of the studies that have been read within the range of the thesis study, it was seen that the most important factor affecting the cavity flow is feedback oscillations. The shear layer is formed when the boundary layer that forms between the free stream and the surface is split from the surface at the cavity's front edge. The resultant shear layer travels along the bay, eventually colliding with the aft wall at the cavity's rear edge. The interaction occurring in this region is accepted as the main acoustic source. The acoustic waves created as a result of this interaction are known to flow towards the cavity's leading-edge, altering the boundary layer's separation period in that location. The interaction between flow-field and the aeroacoustic field is an crucial area of study. This thesis aims to examine and understand the noise caused by cavity flow and the influence of cavity door opening on pressure distribution. Within the scope of the study, a three-dimensional (3D) cavity called M219 in the literature with a L/D ratio of 5 and a W/D ratio of 1 was used, while all analyses were carried out for ReL=10x106 and ReL=13x106 and =0.85. The equations that characterize the motion of fluids called Navier-Stokes Equations want to show both parabolic and hyperbolic characteristics in the transonic region and thus it outshines as a field in which studies are intensified. Detached Eddy Simulation (DES) and Large Eddy Simulation (LES) turbulence models were used throughout the analysis. L is defined as 0.508 meters while D is 0.1016 meters. L represents the cavity length while D represents the cavity depth. Additionally, The International Standard Metric Conditions for air were used. Calculations were executed for approximately 35 convective time scale (CTS). A non-dimensional time step of 10-3 was employed for all calculations and thus it takes 1000 time steps to travel a particle along the cavity length. Pressure values were read and recorded for each time step from 10 probes placed at certain points on the cavity floor. The overall average sound pressure level (OASPL) and power spectral density (PSD) was calculated with the pressure values read and computed sound pressure level (SPL). PSD values were calculated by using Fast Fourier Transform (FFT). The comparison showed that both LES and DES results were in reasonable agreement with experimental results. Passive and active control methods can be used to reduce or control noise generation in cavity flow. Whereas passive control methods are applied by making geometric changes on the body, the energy exchange is applied in active control methods. As the shear layer – trailing edge interaction outshines as the main acoustic source, it has been seen in the literature that configurations that drop this interaction are more successful in preventing noise. Within the scope of this thesis, cavity doors are investigated as a passive control mechanism. In this thesis, OpenFOAM (Open-source Field Operation and Manipulation), an open-source computational fluid dynamics (CFD) tool based on C++ and running on Linux, was used for all calculations. Analyses were conducted on the Faculty of Aeronautics and Astronautics TAI-ITU High-Performance Cluster.
Attitude estimation and magnetic attitude control of a LEO satellite

(Graduate School, 2022-06-17) Eşit, Mehmet ; Hacızade, Cengiz ; Söken, Halil Ersin ; 514191055 ; Defence Technologies

In this thesis, a complete low-cost ADCS is designed for a micro-satellite orbiting in LEO. The attitude determination system of the satellite is considered to be equipped with gyroscopes, TAM and Sun sensor which are the most common attitude sensors for small satellites. For satellite attitude control purposes, magnetorquers are selected as they are cheap, robust and easy to implement. Several static attitude determination algorithms which make use of the vector measurements are described and applied to the attitude determination problem by simulations. A comparison is made between different methods and QUEST algorithm is chosen considering the accuracy, space heritage and robustness. The fine attitude determination system is designed with the integrated scheme in which QUEST and MEKF are combined. In this scheme, QUEST outputs are used to update the filter. This structure provides flexibility with the number of attitude sensors and it can be interchangeably used with star trackers, when available onboard, without changing the filter structure, and also it has a robust structure and fast convergence characteristics. Besides, the multiplicative approach preserves the norm constraint of quaternion and so the filter does not encounter singularity issues by using the quaternion as the attitude parameter. The integrated QUEST/MEKF approach is implemented for the satellite attitude and angular rate estimation. Moreover, the integrated method is compared with the traditional MEKF in terms of convergence speed, accuracy and robustness. Before controlling the attitude, a satellite detumbling method is applied first to reduce the angular rate of the satellite. The Bdot control algorithm is selected as it is easy to apply and it needs only the magnetometer measurements. After detumbling the angular velocity, the attitude is controlled by using MPC approach. Although the magnetic control does not provide three-axis control instantly, the control can be achieved along the orbit in near-polar orbits as the magnetic field is changing over time. Since the magnetic field changes along the orbit, the MPC is chosen as it can predict the future behaviour of the system and adjust the control moment accordingly. Additionally, the magnetometers are fully-calibrated using the TWO-STEP algorithm. Thus, calibrated TAM measurements can be used in both the attitude determination and control algorithms. Eventually, the determination and the control parts of the ADCS are integrated to build a complete system for the satellite. The system is designed such that it first uses Bdot control and then MPC is applied once the spacecraft is detumbled. Integrated QUEST/MEKF outputs are fed to the MPC algorithm and the control moment is calculated by using the estimated states. The simulations are conducted in MATLAB environment for a sun-synchronous LEO micro-satellite.
Güneş enerjisiyle desteklenen İnsansız Hava Aracı tasarım ve üretimi

(Lisansüstü Eğitim Enstitüsü, 2022-06-28) Baykal, Fatih ; Aslan, Ali Rüstem ; 514191044 ; Savunma Teknolojileri

İnsanlar eski dönemlerden beri gökyüzünde uçabilmek için birçok farklı deneme yapmıştır. Bunlardan birçoğu akamete uğramış, ilk başarılı uçuşlar günümüzden yaklaşık 2 asır kadar önce gerçekleşmiştir. O zamandan bugüne geliştirilen teknolojiler ile ses hızını aşan uçaklar üretmek mümkün olmuştur. Üretilen hava araçları kimi zaman sivil amaçlı kimi zaman askeri faaliyetlerde kullanılmaktadır. Güvenlik ve savunma görevleri icra edilirken pilotlar için farklı risklerin var olması, insansız hava araçlarının geliştirilmesine kapı aralamıştır. Önceleri ufak gözetleme görevlerini yerine getirilebilen İHA'lar günümüzde savaş uçaklarının görev yüklerini önemli ölçüde azaltabilecek stratejik araçlar haline gelmiştir. Birçok ülke kendi kaynaklarıyla veya dışardan insansız hava araçları temin edip, güvenlik personellerini tehlikeli ortamlardan uzak tutarak, planlanan görevlerin gerçekleştirilmesi için çabalamaktadır. Böylece insanın içinde olduğu uçuşlardan daha farklı konseptlerdeki savaş senaryolarını ortaya koymak mümkün olmaktadır. Ayrıca günümüz İHA'ları düşman hava savunma sistemlerine sahte hedef olarak saldırıp veya doğrudan kamikaze hücumlar ile onları etkisiz hale getirme kabiliyetlerine sahiptir. Böylece savaş alanında hava üstünlüğü kurmak mümkün olmakta, hava üstünlüğünü kuran taraf kara ve deniz birimleri üzerinde de baskı oluşturabilmektedir. Genel olarak bu yönleriyle değerlendirildiğinde günümüz silahlı insansız hava araçları oyun bozucu özellikleriyle çatışma alanlarında boy göstermektedir. Sivil amaçlı kullanıma bakıldığında özellikle doğa afetleri sonrasında yaşanan arama kurtarma çalışmalarında havadan görüntü almak kritik öneme sahip olduğundan, İHA'lar bu ihtiyacı karşılamaktadır. Karadan ulaşılamayan noktalara havadan gıda ve tıbbı malzeme ikmali yapılmasını mümkün kılarak yine afet bölgeleri veya acil durumlarda insan hayatlarının kurtarılmasına yardımcı olmaktadırlar. Bunun yanında orman yangınları gibi müdahale etmenin veya erken uyarının önem arz ettiği durumlarda İHA'lardan alınan yeryüzü görüntüleri afetle mücadele için büyük önem taşımaktadır. Bunların haricinde haritalama sektöründe, özel bilimsel araştırmalarda, büyük yapı veya tarım projelerinin havadan takibinde de farklı boyutlardaki insansız hava araçları kullanılmaktadır. Orta ve büyük ölçekli insansız hava araçları taşıdıkları faydalı yükler ve görev menzilleri sebebiyle enerji yoğunluğu yüksek yakıtlara ihtitaç duyarlar. Bu sebeple birçoğu karbon temelli yakıtları tüketen güç gruplarına sahiptir. Haliyle uçuş sırasında belli miktarlarda karbon emisyonu ortaya çıkmaktadır. Dünyadaki karbon salınımını azaltmak için politikaların izlendiği günümüzde hava araçlarından çıkan emisyonları en aza indirmek de belirli bir hedef haline getirilebilir. Öte yandan sadece araştırma amaçlı olarak da insansız hava araçlarında hidrojen ve elektrik gibi alternatif enerjilerin kullanılabilmesi için çalışmalar yürütülmektedir. Elektriğin doğrudan enerji kaynağı olarak kullanılmasıysa bataryaların gelişimine bağlıdır. Ticari bataryalar yakın zamanlara kadar 100-250 Ws enerjiyi 1 kg'da depolayabiliyordu. Günümüzde ise bu değer 400 Ws'lere kadar çıkmıştır. Böylece insansız hava araçlarının planlanan görevlerini daha uzun süreyle icra edebilmelerine imkan sağlanmaktadır. Bataryalara daha çok elektrik enerjisi depolayarak uçuş süresini artırabilmenin yanında uçuş için gerekli enerjiyi pv güneş hücrelerinden sağlamak da mümkündür. Pv güneş hücrelerinin tarihte ilk görünümü 20. yüzyılın ortalarına uzanmaktadır. Bu zamandan sonra geçen yaklaşık 20 yılda, tarihler 1974'ü gösterirken pv güneş hücreleriyle desteklenen bir model uçak ABD'de ilk uçuşunu yapmıştır. Sonrasında dünyanın farklı bölgelerindeki kurum ve kuruluşlar mikrodan makroya çok sayıda çalışmaya imza atmışlardır. Elde edilen bu birikimler ile günümüzde güneş enerjisiyle çalışan insansız hava araçları ve insanlı planör uçakları üretkmek mümkün olmuştur. Böylelikle fosil yakıtlara alternatif olan elektrik enerjisiyle uzun süreli uçuşları yapmak mümkün olmaktadır. Ülkemizde üretilen İHA sistemlerine baktığımızda birçoğu fosil yakıtları kullanmaktadır. Elektrik enerjisini kullanan ufak platformlar ise uçuş sürelerinin azlığı sebebiyle uzun süreli gözetleme görevlerini icra edememektedirler. Çoğunlukla sınır karakollarında kullanılan bu elektrikli mini İHA'lar ancak bir güvenlik problemi olduğu takdirde uçurulabilmekte ve kısıtlı süre gözetleme yaparak batarya değişim ihtiyacı duymaktadır. Bu yüzden karakol birlikleri bu batarya değişimleri sırasında görüntü ihtiyacı duyarlarsa daha büyük ölçekli SİHA veya İHA'lar devreye girmektedir. Bu durumda hem gözetleme için harcanan maliyet daha fazla olmakta hemde büyük ölçekli İHA'lar sadece kendilerinin yapabileceği daha stratejik görevleri yerine getirememektedirler. Bu tez çalışması kapsamında güneş enerjisiyle çalışan mini İHA tasarlanıp üretilmesi hedeflenmektedir. İlk etapta güneşli günlerde uçuş için gerekli elektrik enerjisini üzerindeki pv hücrelerden karşılayarak bataryalarından sağlanacak enerjiden daha fazlasıyla uçuşu gerçekleştirip havada kalma süresinin artırılması planlanmaktadır. Böylelikle uzun süreli gözetleme veya takip görevi için icra edilen uçuşları mini elektrikli İHA'lar ile yapmak da mümkün olacaktır. Bahsi geçen konsepteki ticari veya ar-ge İHA projeleri dünyanın birçok bölgesinde çalışılmaktadır. Ülkemiz İHA alanında dünya çapında firmalara ev sahipliği yapmasına rağmen güneş enerjili uçuşlarla ilgili somut çalışmaları görmek pek mümkün olmamıştır. Bundan dolayı aynı zamanda bu çalışmayla Türkiye'deki havacılık ve enerji ar-ge ekosisteminin dikkatinin güneş enerjisiyle uçuş konusuna çekilmesi ve Türkçe literatüre katkı sağlanması amaçlanmaktadır. Çünkü dünya ölçeğindeki birçok projede güneş enerjisiyle uçuş ile günlerce aylarca uçabilecek araçların tasarlanması için çalışmalar yürütülmektedir. Dahası bu çalışmalar neticesinde sanki-uydu araçların üretilmesi ve bunlarla yakın uzaya ulaşılması hedeflenmektedir. Günümüz uydu fırlatma maliyetleri düşünüldüğünde bu araçlar kullanılarak uyduları tamamlayıcı mahiyette bazı görevlerin icra edilebilmesi faydalı olacaktır.
Miniature electrical propulsion system design for cube satellites

(Graduate School, 2022-08-11) Çatal, Egemen ; Aslan, Alim Rüstem ; 514191041 ; Defense Technologies

Cube satellites, also known as cubesats, are compact spacecraft that are made up from 10x10x10cm sized cubes. Each one of these cubes are named units or U for short. Based on mission requirements the size of the cubesat can range from 1U to 27Us. Ever since their establishment in 1999 they have been used for academic and educational purposes. Advancements in the miniature electronic now enables these cubesats to perform at a higher grade and be used for commercial and scientific missions. Their compact nature make them affordable and easy to access. This compactness also means that the power and mass budget is very limited compared to the bigger satellite classes. Thanks to these restraints very few cubesats with propulsion systems have been launched into space to date. A propulsion system has the potential to provide greater missions envelope, extended lifespan, precise control for close formation flying and space debris reduction. Propulsion systems are grouped under two main categories as chemical and electric propulsion systems. Compared to the electrical propulsion systems chemical systems provide greater thrust at the cost of reduced efficiency. Since greater efficiency is vital due to compact nature of the cubesat, electric propulsion systems constitute a tempting solution as a propulsion systems. Among them, RF ion thrusters are viable candidates due to their scalability and simple design. Ion thrusters provide greatest propellant consumption efficiency among electric propulsion systems which makes them very preferable. This study presents the design of an RF ion thruster fit to be used in a cubesat. Theoretical knowledge and calculations are presented and the system is calculated to provide 550 µN of maximum thrust and up to 3000 s of specific imoulse. Design and experimental details are provided and based on these designs the actual model of the thruster is manufactured. Manufactured model was then tested at the Space Technologies Laboratory of Bogazici University (BUSTLab). During the tests it was observed that the ions are successfully accelerated and thrust is generated. Measurements of actual thrust levels and ion beam characteristics are left as future work.
Hibrit kompozitlerde yapıştırma ve sonlu elemanlar analizi

(Lisansüstü Eğitim Enstitüsü, 2022-10-24) Certal, Yasemin ; Bakkal, Mustafa ; 514181017 ; Savunma Teknolojileri

Teknolojinin gelişmesiyle beraber hafif ve yüksek dayanımlı malzemelerin kullanımı ve üretimi artmıştır. Özellikle metal ile beraber kullanılarak elde edilen hibrit yapılar daha çok tercih edilmektedir. Havacılık ve uzay sanayinde asıl amaçlardan birisi de üretilen hava araçlarının hafif olmasıdır. Mukavemet, esneklik, dayanıklılık, kararlılık, hafiflik; ısıya, sıcaklığa ve neme karşı direnç gibi üstün özellikleri nedeniyle havacılık kompozitleri dış uygulamalarda daha fazla tercih edilmektedir. Özellikle uçakların gövdeleri, stabilizatörler, kuyruklar, kanatlar, iniş takımları, ön ve arka kenarlar ile motor kaplamalarında kompozitler yaygın olarak kullanılmaktadır. Hava araçlarında kullanılan metallerin yerine hibrit yapıların kullanılması öngörülmektedir. Bu, bir çok yönden hava aracına fayda sağlamaktadır. Hibrit yapıları birleştirme tekniği olarak ise yapıştırıcı kullanılmıştır. Yapıştırıcı malzeme, yüzeyler arasında kimyasal bağlar yardımıyla bir birleştirici görevi görür. Bağın mukavemeti; yapıştırma prosesine ve yapıştırıcının yüzeyler ile olan uyumuna bağlıdır. İkincil olarak, yapıştırıcı malzeme mikroskobik olarak pürüzlü yüzeylerin girinti ve çıkıntılarına doğru viskoziteye bağlı bir akış gösterir. Yapıştırıcı bu yüzey pürüzlülüğünden destek alarak, mekanik olarak birbirine kenetlenir ve böylelikle yük aktarımına izin verir. Geleneksel birleştirme yöntemlerine göre yapıştırıcının çeşitli avantajları bulunmaktadır. Uçak üretiminde yapıştırma teknolojisinin uygulanması, hafif metal alaşımlarının, fiber takviyeli plastiklerin ve diğer bileşenlerin kullanımından dolayı son derece hafif bir tasarıma izin verir. Bu gelişmelere dayanarak çalışmada yapıştırıcı ile birleştirilmiş hibrit yapılar incelenmiştir. Çalışmada alüminyum, çelik ve titanyum olmak üzere üç farklı metal malzeme kullanılmıştır. Kompozit olarak ise pa 66 %35 cam elyaf takviyeli malzeme kullanılmıştır. Çalışmada kullanılan metal ve kompozit malzemelere zımparalama,kumlama ve lazer desen yüzey pürüzlendirme teknikleri uygulanmıştır. Sade yüzey koşulu ile beraber dört farklı yüzey koşulu için testler yapılmıştır.Ayrıca testler hava araçlarının maruz kalabileceği -40℃ ve +80℃ sıcaklıklarda ve oda sıcaklığında tekrarlanmıştır. Tüm bu parametreler dikkate alınarak hibrit bağlantının mukavemetinde karşılaştırmalar yapılmıştır. Tezin ikinci kısmında ise yapılan deneysel testlerin Abaqus sonlu elemnalar programında yapıştırıcılar için özel olan Kohezif Alan Modelleme(CZM) tekniği kullanarak bağlantının analizi yapılmıştır. Analizden elde edilen sonuçlar ie deneysel testler arasında karşılaştırma yapılmış ve sonuçlar değerlendirilmiştir.
Study of turbomachinery flows using open source analysis software

(Graduate School, 2022-12-19) Çetin, Büşra ; Edis, Fırat Oğuz ; 514191037 ; Defense Technologies

Construction of a proper mesh is a crucial stage of computational studies to obtain acceptable results as the quality of the mesh specifies accuracy, convergence and computational time. Solution is mainly restricted by imperfections on the geometry definition, low mesh quality and relatively coarse mesh structure. OpenFOAM as an open source software, which offers tools to generate grids for the solution domain in addition to execute CFD analysis. For complex geometries, mesh can be constructed by snappyHexMesh utility of OpenFOAM. snappyHexMesh creates an unstructured mesh over a structured state that is generated by blockMesh utility thus it presents an automatic mesh construction tool for engineering applications. In this study, NASA Rotor 37 that is an axial flow, transonic compressor delivering a pressure ratio of 2.1 at design conditions, is analyzed. OpenFOAM was used for both mesh construction and CFD analysis. An unstructured mesh was generated by snappyHexMesh. Since the solution domain contains periodic boundaries, cyclic boundary condition was used. Generation of cyclic BCs on an unstructured mesh are a difficult process by an open source tool as two periodic boundaries must be identical in order to overlap grids on these boundaries. The cyclic surfaces were produced as circular patterns of each other. Quality of the geometry file is also an important factor for mesh construction. Because of unstructured results of snappyHexMesh with non conformal grids, cyclic boundary condition option could not be used solitarily. Non conformal periodic boundaries are matched by cyclicAMI boundary condition options of OpenFOAM that states Arbitrary Mesh Interface and contructs the mesh matching for non overlapping grids. Integration of cyclicAMI was applied by an exclusive OpenFOAM dictionary, createPatchDict. Thus, for obtaining a mesh automatically, geometry files must have high quality, and periodic boundaries must be geometrically identical. Flow field of the rotor was evaluated in terms of total pressure and temperature ratios, and Mach number distributions. Spalart-Allmaras turbulence model was used. Computational results were compared with experimental measurements and other computational results. According to the results, method of preparation of the geometry and construction of the mesh affect accuracy considerably. Total temperature and pressure under predicted in comparison to experiment and other computational studies. It may be caused by rhoSimpleFoam that cannot capture shock, or by low quality geometry. Hence a proper solver and high quality geometry can give satisfying results.
An artificial neural network approach to predict the results of strain gauge measurements in the tensile testing of unidirectional laminated composites

(Graduate School, 2023) Karalar, Anıl Burak ; Balkan, Demet ; 831180 ; Savunma Teknolojileri Ana Bilim Dalı / Savunma Teknolojileri Bilim Dalı

In the area of material science, obtaining material properties by using test methods is an exhausting and an expensive process. Especially in tensile testing, The specimen preparation is time-consuming, and buying specimens is also costly. In order to obtain reliable outcomes, a significant number of test samples incur damage. Therefore, the cost of testing systems is hardly affordable for many researchers, especially in the composite material development process for defense technologies area. New methods in the material testing area are necessary to avoid the economic burden of testing. The main idea of this thesis is to introduce an Artificial Neural Network (ANN) model for predicting a correlation between the device used for testing, and the strain gauges. Furthermore, the strain data obtained from the strain gauges is employed to derive the stress-strain curves essential for determining the material properties. In this thesis, the ANN model predicts the stress-strain curve. Thus, the different algorithms are modeled, and compared to select best algorithm for predicting a stress-strain curve obtained from different tests. Tensile testing is a crucial method for evaluating the mechanical properties of laminated composites. In this study, Artificial Neural Networks (ANN) were employed to analyze and summarize the tensile test results of laminated composites. The ANN models were trained using a dataset consisting of input variables such as displacement (mm), axial force (N), thickness (mm), length (mm), stress (MPa), and strain calculated from the displacement measured by the extensometer, when the output parameter is strain gauge readings. The objective was to develop a predictive model that could accurately estimate these mechanical properties based on the given input variables. Through an iterative training process, the ANN models were able to learn the complex relationships between the input variables and the tensile test results. Once trained, the models could make predictions for unseen laminated composite samples, providing valuable insights into their mechanical behavior without requiring for extensive physical testing. The accuracy and reliability of the ANN models were assessed through various statistical measures such as relative error, mean absolute error, root mean square error, and coefficient of determination and correlation. The results indicated that the developed ANN models were capable of accurately predicting the tensile properties of laminated composites based on the provided input variables. The use of ANN in this study offers several advantages. It provides a faster and more cost-effective alternative to traditional experimental testing, as the models can quickly analyze large amounts of data and provide predictions in real-time. Additionally, ANN models can capture complex nonlinear relationships between the input variables and the tensile properties, which may be challenging to identify using traditional analytical methods.
K bant ve C bant frekans modülasyonlu sürekli dalga radarı tasarımı ve gerçeklenmesi

(Lisansüstü Eğitim Enstitüsü, 2023) Küçükoğlu, Abdulkadir Geylani ; Yeniçeri, Ramazan ; 792999 ; Savunma Teknolojileri Bilim Dalı

Modern sistemler, teknolojik gelişmelerle daha zorlu koşullara uyum sağlamayı gerektirmektedir. Mikrodalga radar sistemleri zorlu çevresel koşullarda etkili ve yüksek doğrulukla çalışabilmektedir. Yüksek çözünürlük ve doğruluk, düşük maliyet ve güç tüketimi, hızlı ölçme yetenekleri sebebiyle frekans modülasyonlu sürekli dalga (FMSD) radar sistemleri günümüzde otomotivden endüstriye birçok alanda tercih edilmektedir. Bu çalışmada K bant frekans modülasyonlu sürekli dalga radarı detaylı olarak analiz edilerek modellenmekte ve gerçeklenmektedir. RF ön uç benzetimleri için AWR Microwave Office programı Visual System Simulation (VSS) benzetim aracı kullanılmaktadır. Bu program ile faz kilitli döngü (ing. Phase Lock Loop), voltaj kontrollü osilatör (ing. Voltage Controlled Oscillator) blokları, güç yükselteç ve düşük gürültülü yükselteç; alçak geçiren ve bant geçiren filtreler; verici ve alıcı antenleri; iletim kanalı, mikser, temel bant filtre ve temel bant yükselteç; analog sayısal dönüştürücü (ing. analog to digital converter) ve hızlı Fourier dönüşüm (ing. fast Fourier transform) modellenmektedir. K bantta tasarlanan donanımda temel FMSD radar blokları; voltaj kontrollü osilatör içeren mikser entegresi baz alınarak, alçak geçiren ve bant geçiren filtreler, anten, güç bölücü, analog filtre ve yükselteçler tasarlanmaktadır. C bantta faz kilitli döngü, düşük gürültülü yükselteç, mikser, güç bölücü, güç yükselteç geliştirme kartları ve anten kullanılarak; alçak geçiren ve bant geçiren filtreler tasarlanarak FMSD radar sistemi oluşturulmaktadır. Kurulan sistem kullanılarak tarama periyodu, faz gürültüsü, harmonik şiddeti, jammer, doppler frekans kayması parametrelerinin radar performansına etkileri incelenmektedir. FPGA ve ADC kullanılarak radar sinyal işleme algoritmasının geliştirilmesi için test verileri toplanmaktadır. Toplanan veriler MATLAB ortamında işlenerek mesafe ve hız hesaplamaları yapılmaktadır. Radar sinyal işleme algoritması sınırlı vuru yanıtı (ing. finite impulse response) bant geçiren filtre, pencereleme, FFT, sabit yanlış alarm oranı (ing. constant false alarm rate) detektörü, hareketli ortalama (ing. moving average) filtre, mesafe ve hız hesaplama algoritmalarını içermektedir. Laboratuvar ortamında yapılan mesafe ölçümleri çeşitli uzunluklarda koaksiyel kablolar kullanılarak gerçekleştirilmektedir. Ek bir faz kilitli döngü geliştirme kartı ile doppler frekans kayması oluşturulmaktadır. Saha testinde huni anten kullanılarak mesafe ölçümü yapılmaktadır.
Developing algorithm for automatic detection of caves using unmanned aerial vehicle data

(Graduate School, 2023) Sağman, Mustafa Bünyamin ; Özcan, Orkun ; 807831 ; Defence Technologies Programme

Caves are underground, naturally occurring hollow spaces that are typically formed by the erosion of rock by water or other natural processes. They can range in size from small passages to vast underground networks, and are home to a wide variety of unique ecosystems and geological features. The exploration and mapping of caves is an important field of study for geologists, biologists, and other researchers, as it can provide valuable insights into the history of the earth and the processes that shape it. Furthermore, finding cave entrances is valueable for defence industry where these capabilities could greatly aid in counter-terrorism effort. Also, it is important to find cave like structures for archaeological exploration because the first settlemenents of humans are caves. In recent years, the use of unmanned aerial vehicles (UAVs) for cave exploration has become increasingly popular, due to their ability to access hard-to-reach areas and collect data from a safe distance. UAVs can be equipped with a range of sensors, such as cameras, Light Detection and Ranging (LIDAR), and thermal imaging, to collect data on the cave environment, including its topography, geology, and biological communities. In the past, the exploration and mapping of caves typically involved physical exploration, with researchers often crawling through small passages to gather data on the cave environment. However, with the advent of UAVs and their ability to collect data from a safe distance, cave exploration has become more efficient and less risky. Data collected by UAVs can include optical data, thermal data, LIDAR data, ground-penetrating radar data, and remote sensing data. Thermal data is particularly useful for cave detection, as cave entrances behave differently from the surrounding environment. For example, during the hottest hour of the day, cave entrances will appear cooler, while during the coldest hour of the day, they will appear warmer. Optical data can also be used to locate caves, by capturing images and labeling them where caves are located to create a dataset for training cave detection deep learning models. Moreover, creating a digital elevation model (DEM) with using LIDAR data is a solution method for exploring caves which could find the hidden caves. Additionally, cave detection systems based on thermal or optical imagery can detect caves that reach the ground surface, they cannot find caves with hidden entrances but ground-penetrating radar can detect underground cavities and sinkholes. Finally, remote sensing with different mutispectral bands and panchromatic bands can be used to identify cave-like structures where the caves are difficult to access. UAVs are becoming an increasingly popular tool for collecting data in the field of cave exploration due to their many advantages over traditional methods. UAVs are easy to manufacture and can be built at a lower cost than manned aircraft. They are also easy to operate and do not put human pilots at risk. Additionally, UAVs have a much lower cost of operation than traditional aircraft, making them a cost-effective choice for researchers and students. UAVs are highly maneuverable, which allows them to access hard-to-reach areas and collect data from a variety of angles and perspectives. This makes it easier to obtain detailed information about the cave environment. Moreover, the collected data has a lower ground sampling distance, which means it can be used to produce more detailed maps and other informative products. In developing an algorithm for automatic detection of caves using UAV data, several key concepts and techniques from the field of computer vision are employed. These include convolutional neural networks (CNNs), which are a type of deep learning algorithm that can learn to recognize patterns in images and other types of data. Optimization methods such as stochastic gradient descent are used to train the CNNs on large datasets of labeled images. Object detection is a common task in computer vision, and involves identifying and localizing objects within an image. Evaluation metrics such as precision and recall are used to measure the performance of the algorithm on test data. In addition, thermal imaging is an important component of the data collected by the UAVs, as it can provide valuable information about the temperature distribution within the cave environment. When used in combination with optical imaging, which captures visible light, thermal imaging can help to distinguish between cave entrances and other types of openings or anomalies. The use of UAV imaging allows for high-resolution data to be collected over large areas quickly and safely, making it an ideal tool for cave exploration and mapping. Several important decisions had to be made to carry out our project. Firstly, a comparison was made between the advantages and disadvantages of different types of UAVs, including rotary wing and fixed wing. After careful consideration, it was decided that a rotary wing UAV would be more appropriate for the project due to its ability to easily land and navigate in wild environments. The DJI Maverick 2 Enterprise was then selected as the UAV of choice, due to its high-resolution camera and thermal imaging capabilities. The location for UAV flight to collect the required data was then decided upon. Cappadocia, Gökova, Oymapinar, and Mersin were selected for the experiments as they are known to have unique geological formations and cave-like structures. Finally, the object detection model YOLOV7 was chosen to analyze the data collected by the UAV. YOLOV7 is a state-of-the-art model that can quickly and accurately identify objects in images. A dataset was generated for training the YOLOV7 model, as there were no existing open-source datasets available. The model was trained to identify cave entrances in the optical images collected by the UAV. An algorithm was then developed to analyze the optical images and identify cave-like structures. Another algorithm was generated for analyzing the thermal images and identifying potential cave entrances. Finally, a decision-making algorithm was developed to combine the results from the optical and thermal imaging analyses to detect the most likely cave entrances. These algorithms were tested and refined using the dataset and imagery collected during the UAV flights in the selected locations. In conclusion, it can be demonstrated that cave entrances can be located using data collected by UAVs as shown in our project. Several advantages are offered by the use of UAVs, such as the ease of use, lower operating costs, and their ability to access hard-to-reach areas. By generating a real-world dataset and developing algorithms for object detection in both optical and thermal imagery, cave-like structures were successfully identified in our experimental sites. Great results were generated even with a limited amount of data, thanks to Deep Learning techniques like YOLOV7. Thermal imaging was found to be an effective way to locate caves due to their characteristic temperature patterns. Astonishing results were achieved by combining optical and thermal imagery with a decision-making algorithm, providing new insights into the detection of underground caves and sinkholes. Overall, the potential of UAV technology and Deep Learning for the identification of cave-like structures and their applications in geological and environmental studies were showcased in our project.
Çok-doğruluklu temsili modelleme ile aeroelastik tasarım optimizasyonu uygulaması

(Lisansüstü Eğitim Enstitüsü, 2023-01-19) Çakmak, Enes ; Nikbay, Melike ; 514181029 ; Savunma Teknolojileri

Hava araçlarının tasarımı, sertifikasyonu ve üretimi oldukça uzun ve zorlu bir süreç gerektirmektedir. Özellikle ticari uçaklarda güvenlik, konfor, performans, çevresel ve ekonomik etkiler gibi pek çok alanda tasarımı etkileyen amaçlar ve kısıtlamalar mevcuttur. Bu nedenle mühendisler tasarım aşamasında pek çok disiplini hesaba katmak durumdadırlar. Bazı disiplinler her ne kadar diğerlerinden ayrı olarak hesaplanabilse de nihai tasarım sürecinde diğer disiplinler ile etkileşime girdiğinden tasarımı bir bütünleşik sistem olarak düşünmek gerekir. Tarihsel süreçte temel disiplinler ile başlayan tasarım çalışmaları gelişen teknoloji ve artan araştırma kabiliyetleri ile yeni ve çok disiplinli çalışma alanlarını ortaya çıkarmıştır. Hava araçlarının tasarımında aerodinamik ve elastik kuvvetler arasındaki etkileşimi inceleyen aeroelastisite ise bu uzmanlıklardan neredeyse en önemlisidir. Hava araçlarının yüksek uçuş güvenliği gerektiren ve yüksek maliyetli yapılar olmalarından dolayı uzun ömürlü ve emniyetli bir şekilde görev yapması beklenmektedir. Bir hava aracı uçuş görevindeyken yoğun aerodinamik yüklere maruz kalır ve bu yükler uçuş sırasında aracın yapısında deformasyonlara yol açar. Aerodinamik yükler sebebi ile oluşabilecek ve uçuş güvenliğini tehdit edebilecek kararsızlıklar yapılarda ölümcül hasarlara sebep olabilmektedir. Bu nedenle ön tasarım sürecinde akışkan ile yapı etkileşiminin hassasiyet ile hesaba katılması oldukça önemlidir. Ancak çoklu fizik içeren disiplinlerin analitik olarak çözümü bir hayli zordur. Bu nedenle bilgisayar destekli sayısal yöntemlere başvurulur. Akışkan ve yapı etkileşim problemlerini sayısal yöntemlerle çözmenin çeşitli yolları vardır. Kısaca bunlar; aynı çözücü içerisinde akış ve yapısal yönetici denklemlerini tek denklem kümesi halinde çözebilen tam bağlaşımlı yaklaşım, yine aynı çözücü içerisinde farklı modüller halinde birbiriyle etkileşen sıkı bağlaşımlı yaklaşım ve farklı çözücülerin birbirleri ile bağlanmasıyla etkileşime girebilen gevşek bağlaşımlı yaklaşımlar olarak özetlenebilir. Bu çalışmada da gevşek bağlaşımlı etkileşim yöntemi benimsenmiş olup akışkan ve yapısal modeller farklı çözücülerde çözülerek aralarında veri alışverişi sağlayan üçüncü bir yazılım kullanılarak hesaplamalar yapılmıştır. Günümüzde her ne kadar hesaplama gücü yüksek bilgisayarlar mevcut olsa da çoklu fizik içeren hesaplamalar oldukça maliyetlidir. Mühendisler bir yandan en yüksek doğrulukta hesaplamalar yaparak en iyi çözüme ulaşmayı hedeflerken bir yandan da hesaplama maliyetlerini düşürmeyi hedeflemektedirler. Havacılığın ilk yıllarında ortaya çıkan ürünlerin zamanla eksiklikleri fark edilerek üzerinde iyileştirmeler yapılarak imkanlar dahilinde en iyi sonuca ulaşılması hedeflenmekteydi, ancak günümüz itibariyle daha ürün tasarım sürecindeyken optimizasyon teknikleri sayesinde hedeflenen en iyi çözümün sayısal olarak belirlenmesi ve test edilmesi mümkün olmaktadır. Ancak başarılı bir optimizasyon sürecinde tasarım uzayındaki değişimlerin iteratif olarak belirlenmesi ve değerlendirilmesi gerektiğinden genellikle bu süreç toplamda yüksek maliyetli hesaplamalar gerektirmektedir. Bu nedenle hedeflenen optimuma ulaşmanın daha düşük maliyetli yolları aranmaktadır. Temelde hesaplama maliyeti yüksek olmayan düşük doğruluklu çözüm ile maliyeti yüksek olan yüksek doğruluklu çözümler arasında yeterli oranda bir korelasyon olduğu düşüncesinden yola çıkarak maliyetli yüksek doğruluklu çözüm kümesini, daha fazla sayıda üretilmiş düşük maliyetli düşük doğruluklu çözümle destekleme yöntemleri aranmıştır. Çok-doğruluklu temsili modelleme yöntemi özellikle optimizasyon ve belirsizlik analizi gibi yoğun veri üretimi gerektiren problemlerde farklı doğruluk seviyelerindeki çözümleri kullanarak fazla sayıda üretilen düşük doğruluklu çözümlerden oluşturulmuş temsili modelin, daha az sayıda üretilen yüksek doğruluklu çözüm ile düzeltilmesi prensibiyle çalışır. Bu sayede bu yöntem hesaplama maliyeti açısından önemli seviyede tasarruf imkanı sunar. Bu tez çalışmasında çok-doğruluklu aeroelastik çözüm kabiliyetinin geliştirilmesi için farklı doğruluk seviyelerindeki akışkan çözücülerinin bir yapısal çözücü ile bağlaşımı gerçekleştirilmiştir. Bu bağlaşımı kullanarak çok-doğruluklu temsili model kurulmuş ve aeroelastik tasarım optimizasyonu gerçekleştirilmesi hedeflenmiştir. Düşük doğruluklu Girdap Kafes Yöntemi çözücüsü olan AVL ve yüksek doğruluklu Euler çözücüsü olan SU2 yazılımlarını, farklı çözücüler arasında veri aktarabilen arayüz modülü pyCAPS yardımıyla Nastran sonlu elemanlar yapısal çözücüsü ile bağlayarak akışkan-yapı etkileşim analizleri yapılmıştır. Çok-doğruluklu temsili modelleme yöntemi olarak CoKriging seçilmiş olup optimizasyon algoritması olarak da Genetik Algoritma kullanılmıştır. Ayrıca çalışma kapsamında temsili modelleme süreçlerinde uyarlanabilir örnekleme yöntemlerinin eklenmesi ile birlikte optimizasyon çalışması daha verimli hale getirilmiştir. Referans model olarak literatürde pek çok disiplinde referans çalışmalarında kullanılması için NASA tarafından paylaşılan Common Research Model uçağının yüksek kanat açıklık oranına sahip versiyonu (uCRM 13.5) kullanılmıştır. Optimizasyon problemini çeşitlendirmek amacıyla biri 3 değişkenden diğeri 6 değişkenden oluşan iki farklı boyutda problem tanımlanmıştır. Bu değişkenler geometrik tasarım değişkenleridir. 3 değişkenli problemde, en az 0,5'lik bir taşıma kuvveti katsayısını zorunlu kılan bir kısıtlamaya tabi olarak sürüklemeyi en aza indirmek hedeflenirken, 6 değişkenli problemde yük faktörü ve moment kısıtlamalarına bağlı olarak yakıt tüketimi minimizasyonu hedeflenmiştir. Tamamlanan uygulama sonuçları ile birlikte, değişen doğruluk seviyelerindeki aeroelastik analizlerde farklı yazılım kodlarını birleştirmek için kullanılan metodoloji başarı ile uygulanmış olup, çok-doğruluklu temsili modelleme temelli optimizasyon yöntemlerinin tasarım süreçlerine entegrasyonu ve avantajları okuyuculara sunulmuştur.
Development of a comprehensive simulation software for spacecraft missions

(Graduate School, 2023-01-27) Gül, Emirhan Eser ; Aslan, Alim Rüstem ; 514191007 ; Defense Technologies

The growth of satellite mission, especially CubeSats, in terms of complexity and capabilities has required the development of dedicated orbit simulation software for mission planning and analysis. This thesis presents the development and uses of a simulation software that will be used to aid in the design of spacecraft missions. The process of developing the software architecture is described in stages from software requirement analysis to test and verification of the final implementation. During a space mission, a spacecraft may be placed in a variety of orbits for different purposes. Preliminary mission design needs to consider all mission phases to meet the needs of more complex missions. To effectively design an orbit, it is important to clearly define the purpose of the orbit and regularly review and reassess this purpose as mission requirements evolve or become more defined. It is also important to consider alternative orbit designs, as there may be multiple options that are viable. For example, a single large satellite in a geosynchronous orbit or a group of smaller satellites in low-Earth orbit may both be effective for communication purposes. Multiple different designs are often compared to find the orbit that best accommodate the mission requirements. There are various criteria that have to be considered according to the mission, such as determining the communication links between satellites and ground stations, and finding the time intervals when there is a pass or eclipse, which allow determining the requirements of communication and power systems. For an Earth-observing satellite, the orbit that has the most revisit time for desired locations and properties of the optical system such as the field of view should be determined. The aim of this work is to make use of the software tools to create a simulation software that provides a framework for efficient analysis and planning of satellite missions that include earth observation, communication, and scientific objectives in order to helps the mission design process by giving the ability to make fast and reliable decisions regarding the satellite system requirements. The developed software implements multiple orbit propagators, with the most prominent being the High-precision Orbit Propagator (HPOP) which takes into account all of the forces that can be modelled so far. However, physics-based models alone are insufficient for accurately predicting orbits and avoiding collisions, as demonstrated by previous collisions caused by such predictions. Our knowledge of the physical world is not sufficient enough to create perfect models as it is near impossible to predict some perturbations precisely, such as solar activity which is only an approximation based on statistical data, as well as the atmosphere models and the area of the satellite that drag force affects, which also change depending on the attitude model. In order to improve the accuracy of these models, a machine-learning approach that utilizes the past flight data is proposed. Models of orbit prediction errors can be learned directly from a large amount of historical data, allowing for predictions without explicitly modeling forces or perturbations. Hence, a neural-networks model was trained and its impact was demonstrated. The software is developed using various programming languages. The user interface is programmed in JavaScript, using HTML and CSS. Orbital analyses and other computation heavy tasks were performed in C++ as it has the benefits of modular design, less resource use and fast execution speed, as well as good portability. Python was used for model training and artificial intelligence methods due to the enormous number of scientific libraries it includes. Electron framework was used to provide cross-platform compatibility. For real-time data visualization in both 2D and 3D, the Cesium framework was implemented using Bing as data provider for satellite imagery and terrain modelling. The simulation results show that the software succeeds in attaining high execution speed and precision. The results indicate that the proposed solution can be useful in reducing time and effort put into the mission design process as well as increase the rate of success for both Earth and interplanetary missions. The developed software can be used for real-world mission design and operations, as a tool for education and engineering studies, and public engagement. The structure of the thesis is as follows. First the mathematical background and celestial relationships that are widely used in mission planning are explained along with the algorithms used to implement them into the software. These include coordinate system transformations, various orbital elements, and time systems. Then orbital propagation is explained starting from two-body motion, which is the basis for all equations of motion, followed by adding perturbations and other forces acting on the satellite to facilitate the high-precision numerical propagator. Analytical propagators that are widely used are explained as well. Then, the design and implementation of a neural-networks model that is trained to improve the accuracy of the numerical propagators is described. The next chapter focuses on the simulation environment and the capabilities of the software. It is possible to easily create mission-specific orbits such as SSO, GEO, and Molniya, predict the visibility of satellites from different locations on the ground, determine the eclipse intervals, compute communication link budget, analyze on-orbit power generation, and perform basic maneuvers within the simulation environment. The software principles, architecture, development process, and user interface design is thoroughly explained as well. Finally, verifications using real data and satellite observations are performed and results are presented, which show that the developed software is ready for real mission use, and possible future developments are discussed.
Propulsion-airframe integration for low-boom supersonic aircraft

(Graduate School, 2023-02-22) İmrak, Rumed ; Nikbay, Melike ; 514191018 ; Defence Technologies

Integration of the propulsion system into the airframe is a critical process of aircraft design, especially for aircraft operating in a supersonic flow regime. Literature shows that the inclusion of a propulsion system in the aircraft design process impacts aerodynamic performance, structural mechanics, and noise characteristics while targeted design requirements become more difficult to be satisfied. This is due to several reasons such as; the external nature of the propulsion system which is generally needed to be designed separately to satisfy engine requirements, the complex flow regime around the engine nacelle, and the sharp velocity and pressure changes required to keep operating an aircraft engine during any possible mission scenario. In order to advance the state of the art in aero-propulsive design optimization research topic; high fidelity, high accuracy computing infrastructures, and accurately scoped design spaces need to be incorporated. One approach is to achieve this objective with a separate design process while locally tailoring aerodynamic shapes of the supersonic inlet and nozzle, limiting design space for nacelle location with trade-offs, and finally, finding the optimal location of the propulsion system on the airframe with an automated design optimization considering sonic boom. In this thesis, a methodology for designing engine components aerodynamically, assembling them as a full-scale nacelle body and finally integrating this geometry into the airframe while considering the sonic boom characteristics of the aircraft, is investigated. First, a validation study is performed to observe the performance of the computational framework. The SU2 open-source multi-physics solver is used for computing the pressure field for the C25D benchmark model. Sonic boom calculations are performed with NASA Langley Research Center's sBOOM software and pressure change through longitudinal distance is compared with literature data. A sufficiently agreeable pressure signature is obtained by considering a disadvantageous calculation environment. A coarser mesh and Euler equations are used which are due to the limited computing power at the very beginning of the research. A small-scale trade-off study is also conducted during this initial phase to examine the effects of nacelle location on pressure signature propagation and noise generated by the aircraft. A representative engine nacelle without internal hollows is positioned in four different locations on the JAXA Wing Body benchmark model with boundary conditions of the C25D's engine. This comparative study concluded that the "shielding" effect of the fuselage is useful for low-boom designs where configurations near the aircraft bodies produced more favorable near-field and propagated pressure signatures. Two novel supersonic, two-dimensional, external-compression inlets are tailored to operate under critical conditions for the given mission requirements. The feasible aerodynamic shape of these air intakes is achieved by using the usual shock relations. These inlet configurations are distinctive by their number of "ramps" to finely tune oblique shock angles in order to concentrate supersonic shocks on the "cowl lip". This operative condition is called "the critical condition" for a supersonic engine inlet. While it is almost impossible to operate an engine inlet under critical conditions during every stage of the mission without a moving surface, the cruise stage of a mission is where this condition must be held for the lowest spillage and highest total pressure recovery. For this purpose, engine inlets are designed to operate under critical conditions for flow parameters that would correspond to the cruise condition of the aircraft. Benchmark geometries shared by NASA for sonic boom prediction workshops are used to determine these flow parameters. The method of characteristics is used to design a minimum-length convergent-divergent duct to be used as a nozzle for the propulsion system to achieve a stable plume shape. Throat and engine plenum areas are based on the provided benchmark model data. Preliminary performance prediction and validation of critical conditions for these inlets and nozzle are done with two-dimensional CFD computations before moving on and integrating full nacelle to the JWB airframe and computing a pressure signature. Two-ramp configuration operates slightly better than a three-ramp by starting under supercritical conditions while maintaining a better total pressure recovery. A 10 dB of difference is computed as an impact of the propulsion system on the perceived loudness level in total as compared to the lean airframe. However, the effect of inlet configuration on the noise level could not be observed as significant since the aircraft body shielded inlet shocks. Preparation to extend design space from rigid aerodynamics to aeroelasticity is started with the inspection of the SU2 code as a fluid-structure interaction driver as it includes a novel elasticity solver which can be coupled to flow solver internally. Examination of the ALE method and methodology of the coupling scheme used in SU2 provides an understanding of FSI methodology in general. The third chapter of the thesis is where previously obtained scientific background, computational experience, and propulsion system configuration are applied in different combinations to C25D and AeroMDO concept aircraft. The first section is reserved for the investigation of the effect of the engine on an aeroelastic aircraft where an in-house developed inner-wing structure at AeroMDO laboratory is used to compute aeroelastic response of C25D concept geometry with its own propulsion system. The maximum displacement value (on the trailing edge of the wing tip) increased 2.04 times due to the pressure changes on the wing for powered configuration. The currently designed wing structural model -which is not in the scope of this thesis- together with the integrated propulsion system, produced relatively low displacement values considering the flight conditions. However, considering that the deformation is doubled, it is important to propose a propulsion system integration in the design of the wing structural model for similar design processes. The second section includes a comparative study to experiment on the position of the nacelle on an aeroelastic aircraft geometry. Representative nacelles are located mid-wing and wing-root to evaluate: displacement of wing structure, nearfield pressure signature and ground-level pressure signature of the aircraft. Considering the engine weight and position, it is observed that the geometry integrated into the middle of the wing increases displacement in the region where it is located but reduces the maximum displacement value as the net force acting on the wing tip is reduced. Lower pressure variations are observed in wing root configuration as a result of the shocks produced by the nacelle located on the wing root being "shielded" by the fuselage. Therefore, wing root geometry is found to be advantageous in terms of noise as it produces lower pressure changes. Finally, an optimization study is conducted using an already optimized in-house low-boom concept airframe. The AeroMDO Lab concept developed a low boom airliner configuration under a TUBITAK-funded scientific project with grant number 218M471. Even though the main scope of this final section is to explain how the propulsion system is located on this airframe, the aerodynamic and structural design procedures of AeroMDO airliner are explained briefly to provide a foundation for engine location optimization study. Two parameters are used to optimize the position of the propulsion system. Namely, longitudinal and later distances of the nacelle. Since the computational burden of engine-activated CFD simulations is drastically high, 19 simulations result is detected as suitable to use while establishing a surrogate model. Then, optimization is performed with the sole purpose of minimizing the noise level produced by the propulsion-integrated airframe. As a result, the noise level of the aircraft is successfully reduced comparing the initial location of the nacelle. Also, the optimum geometry obtained as a result of this study is integrated with the optimum structural model of AeroMDO airliner, and an aeroelastic analysis including all components is performed.
Online loss of control prevention of an agile aircraft: Lyapunov-based dynamic command saturation approach

(Graduate School, 2023-05-17) Altunkaya, Çağrı Ege ; Özkol, İbrahim ; 514211003 ; Savunma Teknolojileri

Over the past few decades, the combat arena has witnessed the updating of military doctrines. In particular, air combat paradigms have been renewed in terms of pioneering air vehicles and air combat tactics. Ancient air-to-air combat maneuvers have been replaced by new, astonishing maneuvers that require more pilot skill and state-of-the-art fighter aircraft in terms of both aerodynamics and flight control. Consequently, advancing maneuvering capability seems to be one of the key features in increasing the survivability of fighter aircraft during dogfights. However, this request brings several prerequisites, including struggling with generated uncertainties because of highly nonlinear aerodynamic characteristics, besides flight dynamics. Another prerequisite is ensuring flight safety throughout the mission, even during the most agile maneuvers, which is the main issue of this study. An agile maneuvering aircraft is inherently expected to perform its mission in the most effective and safe manner, especially a fighter aircraft that carries out outstanding and challenging operations. During these operations, the aircraft is exposed to extremely nonlinear effects sourced from aerodynamics and flight dynamics. As is commonly known, classical linear flight control methods are not capable of dealing with these nonlinear effects because linear flight controllers are designed around an equilibrium point. As the states of the aircraft get far away from that designed equilibrium point, the controller's performance degrades dramatically. Therefore, many nonlinear control methods have been adopted for agile aircraft in the literature and even in the real world. In this study, the incremental nonlinear dynamic inversion technique is adopted for the baseline aircraft, which is the F-16. Moreover, contrary to what is mostly done in the literature, the aircraft control surfaces are treated as independent from each other, as they are in the real world. This means that the system is handled as an over-actuated aircraft, and the six degrees of freedom nonlinear flight dynamic model is constructed as an over-actuated system. Over-actuated systems have control effector distribution such that one specific degree of freedom can be stimulated by more than one control surface. As a consequence, such systems require a control allocation approach to distribute control commands over the control effectors. There are several methods in the literature, but an optimization-based control allocation scheme is utilized to satisfy more than one objective: satisfying control moments required with minimum control effort and minimum drag to increase maneuver performance and avoid control surface saturation. However, the main contribution of the study is loss of control prevention. Operating within the flight envelope does not guarantee flight stability. This means that the aircraft may perform a maneuver within the flight envelope, but the corresponding maneuver may stimulate an unstable behavior. Therefore, the aircraft should perform a maneuver inside the dynamic envelope, not the flight envelope, to ensure flight stability. Consequently, the Lyapunov stability theorem-based control moment redesign and dynamic pilot command saturation methods are proposed to ensure flight stability. Furthermore, an incremental attainable moment set method is proposed to generate controllability boundaries of the aircraft in the next step by using the actuator rate and position limits. The aircraft is allowed to use 90\% of its control authority, and an excessive control moment demand is detected using an incremental attainable moment set. After detecting the control authority violation, Lyapunov-based moment regeneration is activated to obtain the maximum possible control inputs, including the angle of attack, velocity vector bank angle and roll rate. Finally, the recalculated maximum possible angle of attack, velocity vector bank angle and roll rate are fed into the pilot demand saturation. In this way, the pilot is restricted from violating the maximum reachable commands in-flight and dynamically, preventing the loss of control and sustaining the safe and stable maneuver. The paramount importance of this study is to prevent the loss of control without intensive computation or \emph{a priori} knowledge of the aircraft. A broad and high-fidelity aerodynamic model alone is sufficient to achieve each step of the proposal as aforementioned. According to the conclusions presented, the proposed method is quite promising. The aircraft's stable behavior can be maintained even under harsh, excessive, and abrupt maneuver requests.
Savunma sanayii uygulamalarına yönelik grafen takviyeli bor karbür yapıların sps yöntemi ile üretimi ve karakterizasyonu

(Lisansüstü Eğitim Enstitüsü, 2023-06-06) Aydoğan, Yiğit Orkun ; Göller, Gültekin ; 514191083 ; Savunma Teknolojileri

Yüksek balistik özellikliğe ve yüksek kırılma tokluğuna sahip kompozit yapılar uzay ve havacılık gibi kritik uygulamalarda aday malzemeler olarak ön plana çıkmaktadır. Bu alanlara yönelik olarak yeni kompozit yapıların üretilmesi ve özelliklerinin geliştirilmesine yönelik dünya genelinde çok sayıda araştırmalar yapılmıştır ve günümüzde halen bu çalışmalar devam etmektedir. Proje kapsamında elde edilecek olan yeni bileşimler ve üretilecek olan numuneler ile bu alana önemli bir katkı sağlanacağı düşünülmektedir. Malzemeler üzerine yapılan çalışmaların teknolojik gelişmelere katkısı göz ardı edilemeyecek kadar çok olmuştur. Özellikle endüstride ve teknolojide meydana gelen hızlı bir ilerleme arzusu üstün mekanik özelliklere sahip malzemelere duyulan ihtiyacı her geçen gün artırmaktadır. Bu çerçevede dünya üzerindeki bor rezervlerinin % 75'inin ülkemizde olması ve yeni nesil teknoloji malzemesi olarak ilham verici olması, bor ve bileşiklerini önemli kılmaktadır. Dünya bor rezervinin lideri konumunda bulunan Türkiye bor mineralinin dünyadaki en büyük ihracatçısıdır. Stratejik bir değere sahip olan bor minerali Türkiye için geleceğin savunma sanayisine, yüksek teknoloji projelerine, ekonomik olarak kalkınmaya ışık tuttuğu düşünülmektedir. Bor karbür, yüksek pazar hacmine sahip önemli bir bor uç ürünüdür. İleri teknoloji seramik malzemeler arasında bor karbürün vaz geçilmez bir yeri vardır. Bor karbür düşük yoğunluğu, yüksek sertliği, kimyasallara karşı direnci, yüksek nötron absorblama ve ısıya dayanımı gibi özelliklerinden dolayı bir çok sivil ve askeri uygulama alanında kullanılmaktadır. Sert ve hafif olması, muharebe araçlarında zırh olarak, askeri helikopter ve uçaklarda yakıt tankı çevresinde ve pilot kabininde kullanılmaktadır. Sanayi faaliyetlerinde ve üretiminde çok yaygın olarak kullanılan önemli hammaddelere "stratejik maden veya maddeler "adı verilir. Bugün tüm dünyada savunma sanayii alanında teknolojik gelişmelere bağlı olarak ihtiyaç duyulan zırh sistemleri için en çok talep gören malzemelerin başında bor karbür gelmektedir. Bu nedenle bor karbürün özelliklerinin geliştirilmesi adına birçok çalışmalar yapılmıştır. Bor karbür seramiklerinin sahip oldukları yüksek ergime sıcaklıkları sebebiyle döküm yöntemi ile şekillendirilmleri mümkün değildir. Döküm yöntemi ile şekillendirilemeyen bu tür seramik malzemeler sinterleme işlemi ile şekillendirilirler. Sinterleme ön şekillendirmeye tabi tutulan ve yüksek oranda porozite içeren tozların aktif yüzey alanının küçülmesi, partekül temas noktalarının büyümesi ve gözenek şeklinin değişmesi ve porozite hacminin azalması gibi olayları içeren, ısıl olarak aktive edilmiş bir malzeme taşınım olayıdır. Kısacası aktif yüzey alanının difüzyonla beraber küçültülmesi işlemidir. Sinterleme işleminde ana etmen tane yoğunlaşması ve büyümesidir. B4C'nin sinterlemesi ile ilgili literatürde basınçsız, basınçlı ve spark plazma sinterleme yöntemleri mevcuttur. Spark plazma sinterleme (SPS) göreceli olarak yeni bir sentezleme ve sinterleme sistemidir. Spark plazma sinterleme yönteminde iki elektrot arasına yerleştirilen numune, grafit punch vasıtasıyla sıkıştırılıp, numune üzerinden ark geçirilmesiyle yüksek sıcaklıkta yarı ergiyik halde sinterlenir. Spark plazma sinterleme sistemi yüksek darbeli doğru akım ve düşük voltaj ile çalışır. Sıcak presleme, proses, atmosferik sinterleme, ve sıcak izostatik presleme sistemlerine göre düşük sinterleme sıcaklığı, yüksek sinterleme hızı, sinterleme sırasında tane büyümesinin engellenmesi gibi önemli avantajlara sahiptir. Dolayısıyla kısa sürede yüksek teorik yoğunluğa sahip numne üretimine imkan sağlamaktadır. Bu avantajlarından dolayı bu projede B4C'nin sinterlenmesinde SPS yöntemi kullanılmıştır. Üstün fiziksel ve kimyasal özellikleri ile grafen, teknoloji ve bilimin bir çok alanında araştırma faliyetlerinde kullanılmaktadır. Üstün termal, elektronik ve mekanik özelliklerinin kombinasyonu temel bilim ve araştırmaları için geniş bir uygulama alanı sunmaktadır. Özellikle kompozit malzemelerde dolgu malzemesi olarak kullanılabilmesi ve benzersiz özellik kombinasyonu imkanı sunması bir çok araştırmacının dikkatini çekmiştir. Grafen malzemesinin bu üstün özellikleri monolitik seramiklerde ideal bir katkı malzemesi olarak ön görümüştür. Monolitik seramik yapılar yüksek sıcaklık stabilitesi, yüksek mukavemet ve yüksek sertlik gibi fiziksel özellikleriyle yapısal malzeme olarak umut vadediyorken, düşük kırılma tokluğu ve zayıf elektrik iletkenliğine sahiptirler. Bu durumda seramik matrisli kompozit yapıların önemini ortaya çıkarmaktadır. Grafen malzemesinin yüksek mekanik özelllikleri, monolitik seramik yapılar için ideal bir takviye malzemesi yapmaktadır. Tez çalışması kapsamında monolitik bor karbür yapısına hacimce % 0,5, %1, %2, %3 oranlarında grafen takviyesi yapılarak kırılma tokluğu ve sertlik değerlerinin artırılması hedeflenmiştir. Tüm numune üretimleri İTÜ Metalurji ve Malzeme Mühendisliği bölümüne ait 20.000 Amper kapasiteli SPS 7.40 MK VII, SPS Syntex cihazı ile vakum altında 1600oC sıcaklıkta 40 MPa basınç altında 100oC/dk ısıtma hızında 5 dakika boyunca sinterlenerek gerçekleştirilmiştir. Karakterizasyon çalışmaları kapsamında üretilen numuneler için yoğunluk ölçümü, faz analizi (XRD), raman analizi, mikro yapı incelemesi (SEM), ve mekanik özelliklerin tayin edilmesi (sertlik ve kırılma tokluğu) işlemleri yapılmıştır. Yapılan karakterizasyon işlemleri sonucunda monolitik numune için sertlik ve kırılma tokluğu değerleri sırasıyla 29,66 GPa ve 5,27 MPa‧m1/2 olarak tespit edilmiştir. Grafen ilavesi ile en yüksek sertlik hacimce %2 GNP ilave edilen yapıda 38,44 GPa olarak, en yüksek kırılma tokluğu ise 6,83 MPa‧m1/2 olarak belirlenmiştir. Mevcut çalışmada elde edilen 38,4 GPa lık sertlik değeri, savunma sanayii uygulamalarında kullanılan bor karbür seramikleri üzerine yapılan benzer çalışmalardaki sertlik değerleri ile uyumlu/birbirine yakın olduğu gözlemlenmiştir. Düşük yoğunluk, yüksek sertlik ve yüksek kırılma tokluğu özellikleri ile grafen takviyeli bor karbür yapıların savunma sanayii uygulamalarında kullanılma potansiyelinin olduğu değerlendirilmiştir.
AI-based visual odometry implementation on an embedded system

(Graduate School, 2023-06-12) Büyüksolak, Oğuzhan ; Güneş, Ece Olcay ; 514201027 ; Defence Technologies

Navigation technology has always been a critical sub-field for defence technologies. The roots of navigation technology extend to early as 3000 BC year. The early examples of navigation technology were the observation of stars, bird following, etc. In modern days, Global Navigation Satellite Systems(GNSS) and Inertial Navigation System(INS) are widely used in defence technologies. The GNSS and INS systems are included nearly all the modern military platforms and smart munitions. However, they have also practical limitations. Therefore, a companion or alternative to these systems may provide flexibility in the navigational technology for military platforms. Visual odometry is an emerging technique for navigation technologies. The visual odometry technique is a dead reckoning technique, and it is the process of relative pose change estimation from camera images. Processing camera images for visual odometry is a computationally heavy operation. As the military platforms vary between a large scale of different sizes, their power and computational requirements also vary. Also, for expendable platforms like smart munitions, the cost is another important requirement. Embedded visual odometry(VO) implementation may provide a low-power, low cost and small-size alternative or companion positioning system to GNSS and INS. Hence the embedded systems are memory scarce, in this work, a new low-memory footprint neural network-based visual odometry method that is implementable on embedded systems is introduced and evaluated. In this work, firstly, the existing literature for geometry-based and deep learning-based methods was examined. Due to robustness and energy efficiency advantages, it was decided to realize a deep learning-based method, which can be further classified as supervised and unsupervised methods. The supervised learning methods generally require the involvement of other sensors than images and recurrent neural networks. These requirements come with additional computational and power consumption. As a very low-power and real-time system was targeted for this work, an unsupervised learning approach was selected as a training framework. With the ideas from the lightweight convolutional neural networks literature, a neural network namely TinyVO was designed. As monocular techniques provide more robustness and cost advantage than binocular ones, it was decided to use a monocular visual odometry technique in this work. The TinyVO network was trained with a well-known scale consistent unsupervised learning framework. After the training, TinyVO's performance on the KITTI dataset was evaluated. To deploy the neural network, MAX78002 artificial intelligence microcontroller has been chosen as the embedded platform. As MAX78002 supports 8 bits weights, the TinyVO was quantized to 8 bits using the provided MAX78002 software toolset. Also, the toolset supports the known answer test functionality. The known answer test was realized by using a sample from the KITTI dataset. Then, the energy and time consumption per inference values was measured. The resulting neural network, TinyVO enables a monocular visual odometry solution with a low-memory footprint, low power, and reasonable accuracy. To the best of found knowledge, this is the first study that provides a microcontroller-based visual odometry solution.

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