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

ÖgeNumerical and experimental study of fluid structure interaction in a reciprocating piston compressor(Graduate School, 20220114) Coşkun, Umut Can ; Acar, Hayri ; Güneş, Hasan ; 511132113 ; Aeronautics and Astronautics EngineeringConsisting of household refrigerators, cold storages, cold chain logistics, industrial freezers, air conditioners, cryogenics and heat pumps, refrigeration industry are a vital part of many sectors such as food, health care, air conditioning, sports, leisure, production of plastics and chemicals along with electronic data processing centers and scientific research facilities, which can not operate without refrigeration. There are roughly 5 billion in operation refrigeration systems which consumes 20% of the electricity used worldwide, responsible of 7.8% of GHG emission of the world, 500 billion USD cost of annual equipment sale, 15 million of employed people. Around 37% of global warming impact caused by refrigeration is direct emission of fluorinated refrigerants (CFCs, HCFCs and HFCs), 63% is due to indirect emission caused by electricity generation required for refrigeration. Both economic goals of making refrigeration units cheaper, more durable, and environment concerns of making these units more efficient and less hazardous for the world, require meticulous research and study on these refrigeration units. Approximately 40% of refrigeration units consist of domestic refrigeration systems alone where mostly hermetic, reciprocating type compressors are used. Design and improvement of such compressors is a multidisciplinary subject and requires deep understanding of heat and momentum transfer between refrigerant and solid component of compressor which can only be done through scientific investigation, using experimental and numerical techniques. In this thesis study, concerning the advantages of numerical studies, a multiphysics numerical model of flow through the gas line of a household, hermetically sealed, reciprocating piston compressor and the fluid structure interaction around the valve reeds including the contact between deformable parts was developed. Concerning the complexity of the model, the problem divided into several steps and at each step, numerical results are validated with experiments. In the first chapter of this thesis, the motivation behind the thesis study is discussed along with a theoretical background about refrigeration, compressors, fluidstructure interaction and a comprehensive literature survey are summarized to express the position of the thesis study among academic literature and it's novelty. In the second chapter, experimental studies conducted throughout the thesis are presented. Experimental studies divided into two sections. In the first section, the valve reed dynamics are investigated experimentally outside the compressor in multiple test conditions. A test rig is built for this reason, and the displacement of valve reed under constant point load, free oscillation and the impact of valve reed to valve plate from a predeformed form are measured, in order to validate the numerical work. In the second section, the compressor specifications such as cooling capacity, compression work, average refrigerant mass flow rate, along with surface temperature and instantaneous pressure variation from several locations inside the compressor are measured inside a calorimeter setup, to provide boundary conditions and validation for numerical analyses. Numerical work of the thesis study is explained in the third chapter. Modelling the whole compressor gas line between compressor inlet and outlet, including the strong coupled interaction between the refrigerant and deformable solid parts such as valve reeds is too complex of an attempt to do in a single step. Therefore, the numerical problem divided into seven smaller numerical problems and investigated consecutively. At each consecutive steps, problems are isolated, identified, solved and results are validated. The similarity of each step to the final model is increased along with it's complexity as a natural consequence at each consecutive steps. The numerical studies also briefly cover the advantages and disadvantages of using an open source or a commercial multiphysics solver, where OpenFOAM and Ansys Workbench software are utilized for this purpose, respectively. After the simplified steps of the numerical model are completed, the whole gas line of a compressor produced by Arçelik is modelled. The numerical results compared against experimentally obtained data and a good agreement is achieved between them. The developed method is further used for parametric investigation on compressor design to show the capabilities and the benefits of the numerical model. Finally, results of whole thesis study, the experience gained throughout the thesis work and the planned future work are discussed in the final chapter.