Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Subject: search.filters.subject.Genetic algorithms

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Now showing 1 - 3 of 3
  • Master Thesis
    A Genetic Algorithmic Approach To the Differential and Linear Cryptanalysis
    (Izmir Institute of Technology, 1999) Eminağaoğlu, Mete; Koltuksuz, Ahmet Hasan
    The two most well known and recently developed methods in cryptanalysis of DES and DES-like symmetric block ciphers are difTerential and linear cryptanalysis. But these cryptanalytic attacks need to be improved due to the computational performance and storage capacity problems On the other hand, genetic algorithms can be a good solution in cases where the optimum value or near-optimum solutions are sought in complex systems or for non-linear problems. This is a valid situation for the cryptanalysis case where DES and DES-like ciphers are non-linear in structure making dilTerential and linear cryptanalysis a complex system with a very large search landscape and extreme amount of conditional and probabilistic candidates for the key being sought. In this study, a new and promising method wit h bet ter performance is to be developed for differential/linear cryptanalysis of DES and similar symmetric cryptosystems exploiting genetic algorithms' broadened search and optimum finding capacity.
  • Master Thesis
    Optimum Design of Anti-Buckling Behaviour of the Laminated Composites Considering Puck Failure Criterion by Genetic Algorithm
    (Izmir Institute of Technology, 2011) Deveci, Hamza Arda; Artem, Hatice Seçil
    In recent years, fiber-reinforced composite materials have been increasingly used in engineering applications due to their advantages such as strength and weight reduction. Determination of the buckling load capacity of a composite plate under in-plane compressive loads is crucial for the design of composite structures. Accordingly, in this thesis, optimum designs of anti-buckling behavior of 64-layered carbon/epoxy composite plates, which are simply supported on four sides and subject to biaxial compressive in-plane loads, are investigated considering Puck failure criterion by using genetic algorithm (GA). The plates are taken to be symmetric and balanced with continuous fiber angles in the laminate sequences. Critical buckling load factor is taken as objective function and fiber orientations are taken as design variables. The critical buckling load factor is maximized for various loading cases and plate aspect ratios. The optimum designs obtained are controlled layer by layer using Puck failure criterion. A comparison between continuous and discrete plate (laminate in which the orientation angles are limited to the conventional orientations) designs is performed in order to show the reliability of continuous plates. The optimization of 48-layered composite plates has been performed in order to be compared with 64-layered composite plates. The optimum designs considering Puck inter-fiber failure mode C has also been investigated. Finally, a comparative study between Puck and Tsai-Wu failure criteria is performed and the advantage of Puck failure criterion is shown. In conclusion, it is found that the optimum designs of laminated composites considering buckling and ply failure strength depend on loading, loading ratio and plate aspect ratio.
  • Master Thesis
    Stacking Sequences Optimization of the Anti-Buckled Laminated Composites Considering Various Failure Criteria
    (Izmir Institute of Technology, 2011) Söyleyici, Mehmet Umut; Artem, Hatice Seçil
    In recent years, fiber-reinforced composite materials have been mostly used in engineering applications due to advantage of the ratio of strength to weight. Fiberreinforced laminated composites with an optimum stacking sequences have become critical issue especially for defence and automotive industry. In this study, stacking sequences optimization of laminated composites for maximum buckling load factor has been investigated using genetic algorithm (GA). Symmetrical and balanced laminated composite plates with 48 layers graphite/epoxy are considered for optimization process. The designs of composite plates have been investigated for various in-plane loadings and aspect ratios. Fiber orientation angles are chosen as design variables. The optimum designs obtained have been controlled by Tsai-Wu and maximum stress failure criteria. Furthermore, dispersed designs for specific cases have been converted to conventional designs and the advantages and disadvantages of various designs have been examined in terms of buckling resistance. Finally, buckling behaviors of 48- and 64-layered composite plates have been studied under overloaded conditions. In design process, the increase in the reliability of the optimization has been provided independently using a variety of genetic algorithm parameters. All the results have shown that the loading conditions and dimensions of composite plates are significant in stacking sequences optimization of laminated composite materials in terms of maximum critical buckling load factor. Furthermore, it has been seen that the fiber orientation angles determine which failure modes (buckling or static failure criteria) are critical.