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ÖgeEvasive maneuver trajectory optimization for ucav against air to air missile(Graduate School, 2022)Air combat is a form of combat where survival depends on seconds. The delay in communication of unmanned aerial vehicles (UAVs) with pilots in the ground station is the most important shortcoming in terms of survivability. Near-real-time, high-speed communication methods can be developed to overcome this shortcoming but this requires long-term scientific research and engineering which is costly. The less costly solution to this shortcoming is to develop autonomous operation methods for all possible types of missions that onboard computers will process the information collected by the aircraft's sensors and to take countermeasures against the threats without human input. UAVs that will take a more active role in air combat and contribute to air superiority in the future are named unmanned combat aerial vehicles (UCAVs) and are currently under development around the world. Potential threats to be encountered by UCAVs in air combat can be divided into two groups. They are in-line-of-sight (LOS) threats (air-to-air missiles and guns of the enemy aircraft) at short-range and beyond-line-of-sight (BLOS) threats (air-to-air missiles and air defense systems) at long-range. Within the scope of this thesis, threats of beyond-line-of-sight (BLOS) air-to-air missiles will be addressed for evasive maneuvers. In this study, various combat scenarios are generated and trajectory optimization solutions are obtained to perform autonomous evasive maneuvers for UCAVs against air-to-air missiles without human input. To accomplish this objective, an engagement geometry that includes details of UCAV and missile is introduced. This geometry is constructed by employing factors such as line-of-sight (LOS), velocity vectors, angle of attack, flight path angle, and heading angle, which expresses the relative positions of the missile and the UCAV in 3-dimensional space. UCAV and missile are represented as point-mass models using the given geometry. Along with point-mass models, the commonly used Proportional Navigation (PN) method for missiles guidance is implemented. PN is a guidance method that applies acceleration command perpendicular to the instantaneous Line of Sight (LOS) between the missile and the target, which is proportional to the Line of Sight rate and closing velocity. The relative approaching speed of the missile to the target UCAV is defined as closing velocity. An energy formulation is incorporated into the model to calculate the instantaneous energy consumption of the missile. An optimization algorithm is developed so that the UCAV can automatically command the angle of attack and the bank angle to maximize the instantaneous energy consumption of the missile at every time step using the generated model. Optimal trajectories for different engagement scenarios are automatically generated by the optimization algorithm for variable initial conditions such as the missile's heading angle, altitude, and distance from the UCAV. Thus, it is possible to evaluate the evasive maneuver generation performance of the algorithm in different combat scenarios for short, medium, and long-range engagements. To make the missile-UCAV engagement more realistic, some of the engagements have been repeated by adding noise to the missile's velocity and position data. UCAV has performed successful evasive maneuvers to evade the missile in all of its medium/long-range engagements and one of the short-range engagements. This means that adaptive maneuvers suitable for real combat situations are produced for different initial condition sets.
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ÖgeCold gas thruster and controller development for satellite attitude control(Graduate School, 2024-06-13)This paper summarizes the design and application of a cold gas thruster propulsion system for attitude control of satellites and space tugs. The control algorithm's development relies on analyzing data collected through several tests intended for system identification. Therefore, the project highlights the importance of performing real time testing on the physical system along with validating the simulation of the mathematical model. The control mainly relies on PWM signal customized under the special constraints defined by the cold gas thruster characteristics.
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ÖgeAnalysis of meta-gradient incentive algorithm for cooperative behavior in social dilemma problems(Graduate School, 2022)In shared environments, agents are expected to act cooperatively to maximize rewards and achieve objectives. However, it remains as a challenge and an open research problem for self-interested agents to behave cooperatively in Multi-Agent Deep Reinforcement Learning (MARL) environments. Initially, research into multi-agent reinforcement learning focused on developing cooperative policies. However, this requires agents to share their policies with each other, which is sometimes not feasible. An alternative approach involves centralized learning, which relies on having detailed knowledge of agents and their environments. We applied Multi-Agent Proxy Proximal Policy Optimization (MAPPO), a centralized learning method, to investigate the behavior of centralized agents in a custom environment. The environment's objective is to eliminate hostile forces as quickly as feasible. Agents need to collaborate in order to reach the desired outcome. During such military tasks, agents may make strategic decisions or have conflicting objectives. This results in social dilemmas. Rewards and penalties can be utilized to incentivize cooperation when dealing with sequential social dilemmas (SSDs). These incentives can assist agents in learning to cooperate by rewarding them for actions that lead to cooperative outcomes. Learning to Incentivize Others (LIO) is a reward-shaping approach, which uses incentive rewards to encourage cooperation between agents. We analyze the robustness of LIO in the public good game Cleanup under different configurations. Our goal is to identify the sensitive points of LIO and provide insights to enhance meta-gradient based incentive learning. Our primary contribution is to carry out a comprehensive analysis to pinpoint the areas that most require improvement.
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ÖgeIntegrated vehicle control unit development with active safety functions for electric vehicles(Graduate School, 2022)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.
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ÖgeVerification study of wire arc additive manufacturing of titanium alloy TI6AL4V(Graduate School, 2024-08-07)In this thesis, wire arc additive manufacturing (WAAM) method is investigated for production of titanium alloy Ti6Al4V. WAAM is a sub category of directed energy deposition (DED) methods. Tungsten inert gas (TIG) based WAAM technology is utilized for production. 6 axis robotic system, wire feeding unit, welding machine are main elements of the WAAM system used in this thesis. These three equipment are responsible from travel speed, wire feeding speed and heat input, respectively. In addition, flexible inert chamber is also designed and manufactured since titanium's high oxygen affinity. Flexible inert chamber is filled with argon to exclude volume from atmosphere's oxygen. With the help of these equipment, a test wall is printed from Ti6Al4V alloy. It is designed according to required specimen numbers of the standards. Non-destructive tests are conducted for checking porosity or crack presence. Specimens will be extracted from the test wall with water jet cutting method for minimum heat exposure during cutting process. Tensile and fatigue test are conducted as destructive test for obtaining strength data of the material.