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  • Öge
    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 Ancient air-to-air combat maneuvers have been replaced by new, astonishing maneuvers that require more pilot skill and state-of-the-art fighter aircraft in terms of both aerodynamics and flight control.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.
  • Öge
    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.