LEE- Uçak ve Uzay Mühendisliği-Yüksek Lisans
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ÖgeFree routing in high-complexity airspace: impact assessment for environment and aviation stakeholders(Graduate School, 2022-07-06)Global warming is an important phenomenon that is threatening the Earth and the living beings on it. It is affected by the human factors such as fossil fuels, exploitations of forests and livestock. Aviation industry has a part on producing the greenhouse gases causing the climate change. The industries contribution is around 5% to the global warming and it is expected to increase over time regarding its growth. Which is why many organizations are taking action to reduce and mitigate the effects of the aviation to earth temperature. Flightpath 2050 is a documentation for targets defined to reduce the aviation sector's contribution to the climate change. NextGen, SESAR can be counted as initiatives found for the aim. CLIMOP is a project that is coming up with operational improvements aiming to mitigate the climate effects of aviation. There are diverse studies and ideas focusing on reducing aviation's involvement in the long term and short term. While long term mitigations take time for implementation, short term improvements take an important role for reducing overall impact on the climate.Free Routing Airspace is one of the operational improvements that can be counted. Free Routing Airspace (FRA) is a concept introduced by SESAR as an operational improvement and it is defined as an airspace where the users can fly flexible routes with only entry and exit points defined. Evident option to choose in a FRA is the Direct Routes, where the direct path between the entry and exit points is followed by the aircraft. In this study the difference the Direct Route concept makes is assessed considering diverse stakeholders in aviation. Firstly, a high complexity airspace in the ECAC area is selected: EDUU controlled by DFS. It is observed that the air traffic is dense and complex in the area. It is selected as a demonstrative sample of flights to do the comparison. Second, baseline and direct route trajectories are generated using the Trajectory Generation Tool. For the baseline trajectories, ALLFT+ data from EUROCONTROL's DDR database is used and for the direct routes the trajectories are generated directly from the entry and exit points. Then, the different KPIs affecting multiple stakeholders in aviation are determined. The stakeholders are counted as the airlines, passengers, ATC officers and evidently the climate. The KPIs are defined as ATCo workload, number of movements, number of conflicts, routing efficiency, fuel consumption, travel duration, direct operating cost and the greenhouse gas emissions. Emissions of CO2, NOx and H2O are taken into account for the study considering their long-term effects on the earth temperature. xix Once the KPIs are calculated using the models constructed for the baseline and direct route trajectories, the results are compared. It is seen that applying the direct route concept is beneficial for all stakeholders in aviation and it is also better for the climate effects of the industry. This thesis, assesses and compares the impact of the Direct Route application to a high- complexity air space and it demonstrates the improvements that are possible through the practice. It is hoped to serve as a guidance point following the path of optimizing for climate in aviation.
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ÖgeMagnetic attitude control of a nanosatellite(Graduate School, 2022-06-17)In this thesis, a PD and LQR controller is used to control attitude of a nanosatellite with using only magnetorquers. Three different approaches are used for that. Firstly, a deterministic approach is used with the assumption of exact knowledge of data. Secondly, magnetometer, Sun sensor, horizon sensor, and gyroscope are modeled as noisy devices to make the simulations more realistic. Measurements of vector measurement devices are used in TRIAD method to determine attitude. Thirdly, these measurements are filtered with a basic linear Kalman Filter. All these three test cases are used for both controllers with two different satellite models. One of the model is a gravity gradient stable satellite and used as a verification model. The other model is a basic 3U CubeSat orbiting in Sun-synchronous orbit. Tuning the gains of PD controller and Q matrix of LQR is also considered during this thesis. Gain matrices of PD controller is assumed diagonal and tried to be optimized for all the test cases and models. Similarly, Q matrix of LQR controller is considered as diagonal matrix to optimize it. The aim of this optimization process is to obtain a performance increase on attitude control. Also, particle swarm optimization is used for this process. Lastly, magnetorquers, that are used in 3U CubeSat model, are designed in the thesis. One torquerod for two axes and one air core torquer for one axis are designed. The design space of magnetic torquers is created with respect to a literature review for magnetic torquers. Then, the optimized design is selected from this design space with the help of particle swarm optimization. Results of the thesis showed that, achieving 1-2 degree pointing accuracy for each Euler angle with optimized parameters is possible when deterministic case is used. On the other hand, adding noise to measurements and using TRIAD for attitude determination decreased the performance of optimization. It is really hard to work on randomly changed solution space with basic optimization algorithms. While the optimization is running, the run is repeated 10 times to get more stable and high performance results. TRIAD cannot reach high accuracy like deterministic case, but the strategy that is followed for optimization is work for next case. Then, applying Kalman Filter to results of TRIAD allows to an important improvement on attitude control. Kalman Filter almost neglects the effects of noises. Also, in this case the optimized parameters provide similar accuracy as the deterministic approach for some cases. More importantly, it is possible to obtain optimized parameters that are gives stable and accurate results.
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ÖgeInvestigation of mechanical properties of I beam composites developed with 3D woven fabric(Graduate School, 2022-12-02)The need to provide high rigidity and strength for aircraft structures has created a trend, especially toward fiber-reinforced composites. Load transfer in heterogeneous structures such as composites has been one of the most critical issues needs to be improved due to the poor interphase between fiber and matrix. In addition, the weak interface between the layers also causes delamination behavior, which is a dominant damage mechanism. Laminated composites are mostly damaged by delamination and these effects reduce the hardness, strength, and service life of the structures. By preventing the delamination mechanism, the service life and load-carrying capacity of the composites can be improved. However, delamination prevention or retarding methods cause undesirable effects in the aerospace and automotive fields such as thicker and heavier structures. Delamination resistance has been studied to be increased by methods such as tufting, stitching, and z-pinning, but the interest in 3-Dimensional (3D) weaving has increased due to the formation of resin-rich regions and the damage of the yarns and their orientation in different directions. With an innovative approach, 3D weaving, the out-of-plane yarns placed in the fabric increase the toughness of the structure without the need for a secondary process, and also eliminates delamination, which is an undesirable type of failure. Therefore, 3D weaving has gained importance in the aerospace industry, where structures with both light weight and high mechanical properties are preferred. Within the scope of the thesis, it is aimed to produce preforms in I-beam forms with 3D weaving method to be used as load-bearing structural elements in fields such as aerospace and automotive and to produce high-quality composites from preforms. The main aim is to examine and discuss the effect of both 300, 600, and 1200 TEX E-glass fibers and warp density on the mechanical properties of composite beams. Initially, the optimization of a semi-automated weaving machine capable of 3D weaving was studied. To produce preforms with standard weft and warp density and vertical wall height throughout weaving, the features of controlled warp release with servomotors, automatic tamping system, and determining the weft density over the interface have been added to the semi-automated weaving machine. Then, experiments were run to identify the appropriate warp and weft density for 3D preform production with 300, 600, and 1200 TEX E-glass fibers. As a result, the optimized warp density to achieve a stable height of vertical wall of I-beam is 20 cm-1 and weft density is 4 cm-1 for 300 TEX preforms and warp density is 12 cm-1 and weft density is 4 cm-1 for 1200 TEX preforms. Additionally, 600 TEX preforms were woven with a warp density of both 12 cm-1 and 20 cm-1 weft density of 4 cm-1 for a comparison in both data sets of I-beam fabrics. Moreover, the woven I-beam preforms were then manufactured as 3D composites by vacuum infusion prosess. Custom-designed molds were employed to fabricate the I-beam profiled composites with minimum voids and complete wetting having an efficient composite manufacturing process. The thicknesses of the load-bearing vertical walls of the produced composites were 300 TEX (warp/weft density: 20/4 cm-1), 600 TEX (warp/weft density: 12/4 cm-1), 600 TEX (warp/weft density: 20/4 cm-1), and 1200 TEX (warp/weft density: 12/4 cm-1) measured as 2.21 mm, 2.45 mm, 2.62 mm and 2.78 mm, respectively. Thus, the increase in the linear density (TEX) resulted an enhancement on the thickness of the E-glass fibers. Finally, the effect of TEX on the mechanical properties and failure types of composites was investigated by 3-point bending and compression tests. As a result, the development of a semi-automated weaving machine capable of 3D weaving and the production of 3D weaving preforms in I-beam forms using E-glass fibers with different linear densities have been achieved. More design patterns throughout employing the semi-automated weaving instrument is also possible with the flexible design of the system. By a custom-designed mold system, high-quality 3D composites with low void ratio were manufactured by vacuum infusion method. The correlation of linear density of E-glass fibers through both 3-point bending and compression tests were presented the expected trends including the cover factor discussion when 12 and 20 cm-1 warp density was considered for 600 TEX.
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ÖgeGaz türbinli havacılık motorlarında sincap kafes yapısının eksenel yük kapasitesi hesaplarının gerçekleştirilmesi ve yükleme testi ile sonuçların doğrulanması(Lisansüstü Eğitim Enstitüsü, 2022-06-28)Havacılık platformlarında güç veya itki üretme amacıyla gaz türbinli motorlar yaygın olarak kullanılmaktadır. Havacılık platformlarında kullanılan gaz türbinli motorlar turbojet, turbofan, turboprop ve turboşaft olmak üzere dört farklı ana başlığa ayrılmaktadır. Gaz türbinli turbojet motorlar temelde kompresör, yanma odası ve türbin alt modüllerinden oluşan çekirdek motor olarak adlandırılan yapıyı içermektedir. Turbofan motorlarında bu çekirdek motora ilave olarak fan ve düşük basınç türbini, turboşaft motorlarında düşük basınç türbinleri ve turboprop motorlarında düşük basınç türbini, pervane ile pervane dişli kutusu yapıları bulunmaktadır. Bir havacılık motoru ise temelde sabit ve döner parça gruplarından oluşmaktadır. Döner parça grubuna ait olan kompresör ve türbin modüllerinin şaftlar aracılığıyla bütünlüğü sağlanmakta ve bu şaft parçaları da ana şaft rulmanları tarafından mesnetlenmektedir. Gaz türbinli motorlar gibi mekanik yapılarda yapının doğal frekansı ile yapıda oluşan harmonik yüklerin tahrik frekanslarında çakışma gözlemlenebilir ve yapının rezonansa girmesi sonucu şaftlar kırılabilmekte ve tüm yapıyı etkileyen boyutta hasarlar oluşabilmektedir. Yapıda oluşan harmonik yüklerin frekansı tamamen şaftın dönüş hızı ile ilişkilidir ve bu şaftın hızı performans isterlerinden dolayı değiştirilemeyeceği için oluşan yüklerin tahrik frekansı değiştirilememektedir. Doğal frekans ile tahrik frekansının çakışmasını önlemek için ise geriye yapının doğal frekansını değiştirme yöntemi kalmaktadır. Bir yapının doğal frekansı temelde yapının ağırlığına ve direngenliğine bağlıdır. Havacılık yapılarında ağırlık hem platform hem de motor için çok önemli bir tasarım kriteri olduğu için yapının doğal frekansının değiştirilmesi için en uygun çözüm yöntemi yapının direngenliğini değiştirmek olarak belirlenmiştir. Havacılık motorlarında yapının direngenliğini değiştirmek için rulman mesnet noktalarında yüksek esnekliğe sahip sincap kafes parçaları kullanılmaktadır. Yüksek esnekliğe yani düşük radyal katılık değerine sahip bu sincap kafes parçaları sayesinde şaftların mesnet noktalarındaki radyal katılık değeri kolaylıkla ayarlanabilmekte ve rotor dinamik analizleri sonucu yapının çalışma aralığında rezonansın oluşumunun engellenmesi amacıyla belirlenen radyal katılık değeri bu parça ile kolaylıkla yapıya yansıtılabilmektedir. Sincap kafes parçaları radyal katılık isterini kiriş adı verilen boşluklu yapıdaki tasarımları ile sağlamaktadır. Tasarlanan kiriş unsurları yapının geneline kıyasla düşük kesit alanına sahiptir. Sincap kafes parçaları aynı zamanda rulman yataklama elemanları oldukları için rulmana etkiyen tüm eksenel ve radyal yükleri taşıyıcı yapıya aktarmaktadır. Bu sebeple normal operasyon yüklerinin yanında kanatçık kopması gibi hasar senaryolarındaki yüksek yüklere de maruz kalmaktadır. Bu tez çalışması kapsamında maksimum 3250 N/mm radyal katılık isterine göre tasarlanmış bir sincap kafes parçasının katılık doğrulama ve elastik plastik analizleriyle beraber doğrusal olmayan öz değer burkulma analizleri gerçekleştirilmiş ve elde edilen sonuçlar parça seviyesi yapılan yükleme test sonuçları ile kıyaslanmıştır. Yapının ilk boyutlandırması el hesaplarına göre gerçekleştirildiği için basit bir statik analiz modeli ile yapının radyal katılık değeri doğrulanmıştır. Ardından elastik plastik dayanım analizleri ile yapıda kopma veya kırılmaların gerçekleşeceği eksenel yük limiti elde edilmiştir. Kiriş yapıları radyal katılık isterini sağlamak amacıyla ince ve uzun yapıda tasarlandığı için yapıda kırılma limitine ulaşılmadan burkulma hata modunun gerçekleşme ihtimali de bulunmaktadır. Bu sebepten dolayı statik elastik plastik analizlerinin ardından tasarlanmış olan parça için sincap kafes özelinde öz değer burkulma analizi gerçekleştirilmiştir. Yapılan çalışmalarda 3250 N/mm veya daha düşük radyal katılık değerine sahip sincap kafesi için gerçekleştirilen elastik plastik dayanım analizleri sonucu parçada 51,47 kN ve öz değer burkulma analizleri sonucunda 135,15 kN eksenel yük kapasitesi tespit edilmiştir. Sonlu elemanlar yöntemi ile gerçekleştirilen analiz sonuçlarına göre öz değer burkulma analizinden elde edilen değer, elastik plastik analizinden elde edilen değerden yüksek olduğu için parça burkulma hata moduna girmeyecek ve 51,47 kN eksenel yüke maruz kaldığında parça malzemesinin maksimum çekme dayanım sınırı aşılacağı için parça kırılacaktır. Parça seviyesi gerçekleştirilen eksenel yük taşıma kapasitesi testleri iki benzer numune ile gerçekleştirilmiş ve iki numunede 62,88 kN ve 60,87 kN mertebelerinde eksenel yük taşıma kapasitesi tespit edilmiştir. İki numune arasında eksenel yük taşıma kapasitesi arasında yaklaşık olarak %3,19 mertebesinde fark bulunmaktadır. Aynı ham malzeme kullanılarak üretilen bu sincap kafes test numuneleri arasında oluşan farkın ana sebebi parçaların imalat toleransları olduğu düşünülmektedir. Analizlerden elde edilen eksenel dayanım limiti ile testlerden elde edilen eksenel yük taşıma kapasitesi arasında yaklaşık olarak %15,4 fark bulunmaktadır. Testlerde elde edilen sonuçların analiz sonuçlarından belirtilen oranda yüksek çıkmasının iki ana sebebi bulunmaktadır. Bunlardan birincisi analizlerde minimum dayanım özelliklerine sahip malzeme verilerinin kullanılmasıdır. Potansiyel ikinci sebep ise analiz modellerinde nominal boyutlara sahip sincap kafes modelinin kullanılması fakat testlerde imalat toleransları sebebiyle bir miktar daha kalın kiriş geometrilerinin kullanılabilmiş olma durumudur. Bu iki potansiyel sebep göz önünde bulundurulduğunda testlerde daha yüksek dayanım sonuçlarının elde edilmesi temellendirilebilmektedir. Gelecekte ihtiyaç duyulabilecek tasarım iterasyonları veya yeni tasarımlar için dayanım analizleri sonuçlarının güvenlik katsayısının yüksek güvenilirliği olduğu sonucuna varılmış olup yapılacak tasarımlar için gerçekleştirilecek analizlerin bir test ile tekrardan doğrulama ihtiyacı olmadığı sonucuna varılmıştır.
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ÖgeDevelopment and testing novel guidance algorithms for visual drone interception(Graduate School, 2024-06-13)This study tackles the challenge of guiding a quadrotor to intercept fast-moving targets visual and radar feedback by Visual Inertial Odometry or GPS respectively. Proposed system, designed as a counter UAV solution, utilizes onboard camera and radar information of the aerial threat. Target interception process has been divided into two parts. One is pre-terminal phase guidance where target information comes from radar feedback. Unless the target has not been seen at the camera, interceptor guided from radar feedback. Once the target is detected by the camera, the quadrotor switches to terminal phase guidance which is guiding counter drone to aerial target by visual feedback. For pre-terminal guidance, two different algorithms were developed. A Model Predictive Control based guidance algorithm has been designed for pre-terminal guidance. For pre-terminal guidance, parallel interceptions (toward the head or back) provide robustness to inevitable visual processing latency in terminal phase compared to lateral engagements. By addressing these issues, the proposed methodology mainly utilizes Model Predictive Control (MPC) method with added terminal constraints to satisfy engagement at the desired angle. While formulating the MPC, the objective function in the MPC is modified to reduce the interceptor's requirement for maneuvering at the end of the trajectory. MPC prediction horizon is calculated by considering vehicle limits to satisfy the feasibility of the problem. Another method is we use Bezier Splines to guide the quadrotor. Since quadrotors has limited onboard computational power, MPC might not be practical for some cases. By ensuring continuity with Bezier Splines, the system determines the optimal interception direction (towards the head or tail) and calculates the time-to-go, considering in the target's position and velocity along with the interceptor's kinematic constraints. This method specifically addresses latency issues in target detection, crucial for intercepting high-speed targets effectively. Moreover, the delays introduced by target detection and localization pose significant challenges, particularly for small quadrotors with limited computational power. The proposed approach aims to achieve parallel engagement with the target's velocity vector, whether from the front or rear, thus minimizing delays and overcoming visual tracking difficulties before target is detected by onboard camera. This strategy reduces lateral acceleration within the image frame during the final stages of interception, resulting in smaller miss distances. This outcome is consistent with established guidance literature, which recognizes the advantages of reduced acceleration at the end of the interception path. When the target is detected by camera using object detection algorithms, terminal phase guidance is initiated. For detecting aerial threats, the object detection algorithm You Only Look Once (YOLO) is used. Maintaining detection and tracking by camera can be interrupted due to limitations such as motion blur, noise in the image and getting out of the camera field of view. When detection is interrupted, Kalman Filter is used for prediction of the target. For image based guidance we utilized proportional guidance with some modifications. For this work we assume that no stabilizing mechanism that preserve orientation of the camera is used. Since no stabilizing mechanism is used for the camera, we formulized propotional guidance rules in roll and pitch stabilized frame in order not to being affected from camera orientation. We employed two distinct navigation methods: GPS-based navigation and Visual Inertial Navigation for navigating towards to target at the pre-terminal phase. The well-established open-source ArduPilot platform was utilized for GPS-based navigation, while VINS-Mono was implemented for Visual Inertial Navigation. As for controllers, due to the differing frequencies of estimated odometry data from these systems, different position controllers were employed for each navigation solution. The ArduPilot built-in controller was utilized for GPS-based navigation, whereas a custom controller was designed and flight-tested for handling VIO feedback. The aforementioned navigation and control methods allowed us to compare and evaluate their performance in different scenarios. The GPS-based navigation provided a reliable and accurate solution in environments with clear GPS signals, while the Visual Inertial Navigation offered a robust alternative in situations where GPS signals were weak or unavailable. The custom controller designed for VIO feedback was optimized to handle the unique characteristics of visual inertial data, ensuring smooth and precise control of the quadrotor. Through this approach, we were able to develop a comprehensive navigation system that can adapt to various operational conditions, enhancing the overall reliability and effectiveness of the quadrotor's guidance and control. Finally, real world flight tests were conducted for assessing overall performance of the system. To evaluate the performance of the GPS-based and VIO-base navigation algorithms, interception flights tests were conducted separately and the performance of the guidance algorithm was assessed accordingly. In real-world flight tests, we tested the use of Bezier splines in the pre-terminal along and image-based visual servoing for the terminal phase. In doing so, we examined the use of GPS-based and VIO based navigation algorithms. Results show performance of the proposed methodology.