Master Degree / Yüksek Lisans Tezleri

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

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Access Right: Embargoed AccessDepartment: search.filters.department.Thesis (Master)--İzmir Institute of Technology, Civil Engineering

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Now showing 1 - 5 of 5
  • Master Thesis
    Topology Optimization of Non-Linear Elastic Microstructures
    (01. Izmir Institute of Technology, 2023) Güven, Murat; Özdemir, İzzet
    Topology optimization (TO) is used in a broad spectrum of engineering disciplines ranging from aerospace to civil engineering. A particular sub-field where topology optimization has been very instrumental is the design of microstructures that yield specific macroscopic properties, such as negative Poisson's ratio and negative magnetic permeability. In this thesis, based on a recently proposed method for nonlinear homogenization, a framework for topology optimization of nonlinear elastic microstructures is developed and implemented as a computer program using the Julia programming language. Following a plane strain formulation, a two-dimensional unit cell with periodic boundary conditions is used in combination with a neo-Hookean elastic material response. By exploiting the symmetry properties of the resulting orthotropic microstructure, it is shown that the computational domain can be reduced, and half of the original discretization is sufficient to carry out the optimization task. The obtained topologies from the developed computer program, the linear and nonlinear response comparison, and the computational gain achieved through domain reduction are presented along with the experiments on proof-of-concept type uni-axial tests.
  • Master Thesis
    Numerical Modelling of Failure in 3d Quasi-Brittle Unreinforced Structural Components
    (Izmir Institute of Technology, 2022) Kaçmaz, Bekir; Özdemir, İzzet
    Concrete has been one of the most commonly used modern structural material with quasi-brittle response. Because of its wide usage, numerical prediction of crack path and failure of structural components made of concrete and reinforced concrete has a great importance. To achieve this goal, a wide range of techniques have been introduced by treating fracture differently. In addition, the development of successful element formulations in analysis of 3D structural components has also been an active research topic. Several formulations have been proposed as an alternative to the conventional Lagrangian elements in recent years. In this thesis, localizing implicit gradient damage model and an isogemetric tetrahedral element are combined to investigate failure of 3D quasi-brittle unreinforced structural components. 10 noded B´ezier tetrahedral element is implemented to commercial finite element software Abaqus through user defined element subroutine, UEL. The implementation is validated by using two benchmark problems with nearly incompressible linear elastic and elasto-plastic material behaviors. After validating the implemented element, the formulation is extended such that localizing implicit gradient damage model is embedded within the isogeometric element formulation. Resulting two field formulation is tested on 3D experimental studies that exhibit complex fracture propagation due to combined torsional and bending moments. The sufficiency of the implemented two field formulation is verified by comparing obtained results with the experimental ones in terms of both force versus displacement responses and resulting crack paths.
  • Master Thesis
    Crystal Plasticity Inspired Modelling of Fibre Reinforced Composites
    (Izmir Institute of Technology, 2022) Dizman, Emir Aybars; Özdemir, İzzet
    There is an increasing demand in carbon fibre reinforced (CFR) composites primarily due to their high strength-to-weight ratio. Although their single-ply behaviour is rather brittle (as compared to metals), by reducing the ply thickness and stacking differently oriented plies, brittleness is suppressed, and a ductile behaviour similar to metals is achieved. In this thesis, a recently proposed material model inspired by crystal plasticity is reconsidered and implemented in an implicit finite element solution framework. To this end, a user-defined element is developed in a geometrically non-linear continuum setting and implemented in commercial finite element software Abaqus through UEL (Userdefined ELement) subroutine. The model is validated by analytical solutions derived for simple shear cases and two experiments for different loading cases from the literature. The model is capable of predicting stress-strain response well in cases where matrix plasticity is dominant. Moreover, a parametric study on the cross-ply shear specimen is conducted to investigate the influence of different material parameters. In the last part, the model is extended by a continuum scale damage in the matrix and degradation in elastic material properties. The predictive capabilities of the damage extended model are assessed by re-analyzing the cross-ply shear test.
  • Master Thesis
    Simulation of Water Resources of Tahtalı-Seferihisar Sub-Basin Based on Weap Model
    (Izmir Institute of Technology, 2021) Karahan, Sait Mutlu; Elçi, Şebnem
    Water is a vital resource for humanity and nature, and the lack of water affects life in all areas. Today, problems such as the inability to protect the status of existing water resources and excessive water withdrawal cause the amount of water to decrease day by day. In addition, conditions such as urbanization and industrialization and the resulting population increase, deterioration of water quality due to chemicals used in agricultural activities, and climate change affect the availability of water resources negatively. In this study, a basin-based water management study was carried out by applying the "Integrated Water Resources Management" approach to the Tahtalı-Seferihisar Sub-Basin located in Turkey, where it is expected to experience water stress in the future. The hydrological (precipitation, flow, evaporation) data of the water resources that are important for the basin and İzmir (Tahtalı, Seferihisar, Ürkmez, and Kavakdere Dams) were used to predict the availability of water resources in the future using the WEAP (Water Evaluation and Planning System) program, and several possible scenarios for water demands/supplies were analyzed. Under these situations, the water budget balances expected to occur 2050 have been estimated. Basically, seven different scenarios were created to transfer possible future possibilities to the program: Reference Scenario, Best Case Scenario, Worst Case Scenario, Report Consumption Scenario, Return Flow Scenario, Population Projection Scenario and Various Forecast Scenario. The water balances that can be obtained under different conditions in each scenario were calculated and compared with each other.
  • Master Thesis
    Numerical Modeling of the Artificial Destratification of the Thermally Stratified Water Column by Air Diffusers
    (01. Izmir Institute of Technology, 2021) Bahadıroğlu, Nisa; Elçi, Şebnem
    Reservoirs have essential roles in water management due to the large areas of use. In a reservoir, the structure of the temperature profile in the vertical water column mainly controls the vertical distribution of heat, dissolved substances, and nutrients. Thermal stratification in the water column can lead to an anoxic and poor quality water source. Artificial destratification has been widely used to improve water quality in thermally stratified water sources. This study focuses on the numerical modeling of artificial destratification of thermally stratified water columns by air diffusers to improve the water quality of reservoirs. Firstly, destratification experiments were performed to verify the numerical models. In the experiments, the effects of air diffuser hole diameter, air flow rate, and the number and configuration of holes on the diffuser on destratification time and efficiency were observed. The second part of the study comprised the numerical modeling of hydrodynamics during the destratification of thermally stratified water columns by air diffusers. ANSYS Fluent software is utilized for the simulation of the hydrodynamic processes. Model options for multiphase flows, boundary conditions, and turbulence; and their comparison with experimental studies are discussed. The Eulerian multiphase model and k-ω turbulence model were found to be suitable for this study. In the final part, the numerical model was verified with the experiments. Based on the error analysis of comparisons of the model and observations, the best configuration of air diffuser is proposed, and the numerical model was found to be successful in simulating the destratification of thermally stratified water columns by air diffuser.