Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Hydrodynamic Investigation of an Innovative Floating Platform for Offshore Wind Turbines(01. Izmir Institute of Technology, 2022) Özbahçeci, Bergüzar; Özbahçeci, Bergüzar; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyWith the realization of the potential of wind energy in deep water, interest in floating platforms is increasing. In this study, the hydrodynamic behavior of offshore floating wind turbines was examined experimentally and numerically. This study is the first small-scale experimental model study on floating offshore wind turbines in Turkey. Experiments were carried out in the wave channel with dimensions of 40.0m×1.0m×1.4m in the hydraulic laboratory of the IZTECH Civil Engineering Department. A new floating platform developed through a Tübitak project was tested under various wave and extreme wind conditions. Responses of the turbine and platform system and the tensions in the mooring chains were measured. Free decay, hydrostatic, quasi-static, and regular and irregular wave and wind tests were performed. Results were compared with the results of the existing spar platform model tests under the same test conditions. It was concluded that the innovative platform was more stable than the spar platform, especially in terms of rotation in the y direction, which is critical for stable energy generation and fatigue loads. The new platform, together with the turbine and the mooring lines, was also modeled numerically using a potential theory-based program. Experimental free decay tests were used to calibrate the numerical model. After calibration, regular and irregular wave test results were used for the validation. Agreement between the numerical and experimental model studies showed that the numerical model of the innovative floating platform was verified and could be used to develop and examine the platform on a prototype scale.Master Thesis Investigation of Coastal Flood Problem in İzmir Bay(Izmir Institute of Technology, 2022) Özbahçeci, Bergüzar; Özbahçeci, Bergüzar; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyIzmir, with its long coastline, is one of Turkey's leading tourism and trade cities. The coastal flood is an important problem in İzmir Bay. The literature review shows that there is no study that covers all the elements of the problem such as wind and wave climate, fluctuations in the sea level and coastal flood calculations in İzmir Bay. In this study, the ERA5 wind dataset developed by the European Center for Medium Range Weather Forecasts was used to determine extreme wind speeds. The data were verified using in-situ wind measurements data. Then, the fluctuations in sea water level caused by astronomic and atmospheric effects such as tides, wind and wave set-up and barometric effects were examined by the analysis of sea water level measurement data of the Izmir Metropolitan Municipality in Bostanlı and Pasaport and the tide gauge station data of the General Directorate of Mapping in Mentes. The long-term trend of sea level was examined using Theil-Sen and the line of best-fit methods. Then, the reliability of the trends was demonstrated by performing the Mann-Kendal test. Calculated extreme wind speeds and sea level fluctuations were taken into account to estimate the waves in front of coastal protection structures using a wave model called SWAN. Then, in order to predict the coastal flood amounts, the wave overtopping was calculated by the artificial neural network method. It is concluded that the most sensitive places in İzmir Bay in terms of coastal floods are the areas protected by vertical walls.Master Thesis Wave Generation and Analysis in the Laboratory Wave Channel To Conduct Experiments on the Numerically Modeled Spar Type Floating Wind Turbine(01. Izmir Institute of Technology, 2020) Özbahçeci, Bergüzar; Aktaş, Kadir; Özbahçeci, Bergüzar; 01. Izmir Institute of Technology; 03.03. Department of Civil Engineering; 03. Faculty of EngineeringThe oceans offer immense potential for harvesting sustainable wind energy, with stronger and steadier winds for locations further offshore. Since the feasibility of fixed-bottom offshore wind turbines decreases with increasing water depth, floating offshore wind turbines (FOWT) becomes a promising field of study. As part of a TÜBİTAK project (217M451) that investigates the dynamic performance of different FOWT designs under wind and wave loads, the necessary laboratory wave generation, analysis, and test set-up to conduct physical model experiments of a spar-type FOWT model is established in this study. An investigation of the wavemaker theory yielded that using first-order wavemaker solutions in the laboratory leads to the generation of spurious harmonic waves that do not appear in natural waves. Therefore, the second-order solutions are applied to the piston-type wave generator for a closer approximation of natural waves in laboratory conditions. A numerical model investigation of a reference spar-type FOWT is conducted to gain insights into spar design using ANSYS AQWA. The results indicate that the spar model dynamic responses are susceptible to low-frequency waves in pitch and surge degrees of freedom as its natural frequency lies in that region which further emphasizes the importance of generating laboratory waves using second-order wavemaker theory. Additionally, a spar-type floating platform is modeled at the 1/40 Froude scale, to use in the hydraulic model experiments. The wave measurement set-up is fully implemented and theoretically generated waves are measured for validation. In conclusion, regular and irregular wave generation and wave analysis in the time and the frequency domain could be possible in the wave channel of IZTECH Civil Engineering Hydraulic Laboratory.Master Thesis Numerical Examination of Floating Offshore Wind Turbine and Development of an Innovative Floating Platform Design(Izmir Institute of Technology, 2020) Alkarem, Yüksel; Özbahçeci, Bergüzar; Özbahçeci, Bergüzar; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyHarvesting offshore wind energy has been a primary stimulus for research recently as more shreds of evidence show the highly unexploited potential it carries. As water depth increases, fixed-bottom foundations become impractical and floating solutions must be adopted for offshore wind turbines. The underlying causes of high demands to reach accurate numerical simulation of floating offshore wind turbines are a plethora. The system's nonlinearities impose a serious challenge on the estimation of system responses, power production, and fatigue loading. Proper simulation of environmental stochastic loading from wind and wave plays a critical role in the analysis of such systems. The floating platforms govern the integrity of the entire system. There are different kinds of existing platforms like semi-submersible, spar, tension leg, etc. However, attempts to reduce hydrodynamic and aerodynamic-induced mean and dynamic excitations continue. This study examines the performance of a semi-submersible platform numerically using a hydro-aero coupled model and compares the results with the benchmark experimental data and other numerical model studies. A comparative study shows the present model depending on the second-order potential theory, and the dynamics of the mooring cables agrees well with the experimental results. A spar type platform is also modeled for mid-depth conditions. Moreover, a novel floating platform is developed and compared to existing alternatives in the field. The proposed platform achieves better stability in terms of mean offsets and dynamic oscillations, especially in pitch at extreme conditions. Another extinct feature of the design is the diminished tensile strain in the mooring lines for a relatively shorter cable length and equal linearized horizontal stiffness.Master Thesis Nearshore Wave Prediction Modeling for the Southern-West Coasts of the Black Sea and Comparison With the Wave Measurement Data(Izmir Institute of Technology, 2019) Güler, Muzaffer; Özbahçeci, Bergüzar; Özbahçeci, Bergüzar; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyWhile waves propagate towards shallow areas where most of the coastal structures are constructed, their properties like wave height and direction may change. The change in the wave properties in shallow areas called wave transformation may happen due to a decrease in water depth, sea bottom configurations or some obstacles like islands. Therefore, it should be calculated to find the wave properties used in coastal engineering projects. In this study, the main purpose is to model the waves in the near-shore region of the Filyos coast in Zonguldak province of Turkey by a 3rd generation nearshore wave model, SWAN (Simulating Waves Nearshore). The newest re-analysis data, ERA5, of The European Centre for Medium-Range Weather Forecasts (ECMWF) are used as SWAN model input in deep water. The data are calibrated with satellite radar altimeter data before using the model input data. One of the targets of the study is to verify the developed model using data of an in-situ measurement campaign organized by the Turkish Ministry of Transport. A verification study is performed using not only all data but also using the storm data with higher waves. For the selected storms, statistical and spectral analyses of the raw data are also performed. Results of the verification study show that wave predictions obtained from the developed nearshore wave model using SWAN fit to in-situ measurements well. Results are also compared with the previous studies and it is concluded that error results are much better for the wave period.Master Thesis Derivation of Century-Based Wave Climate and Extreme Wave Analysis Along Turkish Coasts(Izmir Institute of Technology, 2019) Turgut, Ahmet Rıza; Özbahçeci, Bergüzar; Özbahçeci, Bergüzar; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyReliable and long-term wave data are essential for the design of almost all coastal and marine structures. In this study, the wave climate along the Turkish coasts was derived based on a century long data of European Centre for Medium-Range Weather Forecasts. For this purpose, firstly, the data set was calibrated and verified by using satellite and in-situ measurements. Then the design waves corresponding to different return periods were determined by extreme statistics. Therefore, a new and reliable design wave height data along the Turkish coasts have been provided for the designers and applicants. Results were compared with Wind and Deep Water Wave Atlas Along the Turkish Coasts (Ozhan and Abdalla, 2002). The comparison results indicate that the design wave heights provided by the Atlas are higher than the current study, especially in the Aegean Sea. Moreover, the effect of theoretical distribution function and the data number were investigated on the design wave height. Design wave heights were recalculated by best fitting distribution function and it was shown that distribution function may affect the design wave height. It was also concluded that when the wave data used in extreme value analysis was less than 30 years, the error increased in the estimation of the design wave height with both 50 and 100 years return periods. Besides, by using calibrated and the verified century-long wave climate data it was shown that there was an increasing trend in the annual mean and maximum wave heights along the Turkish coasts.Master Thesis Steady and Unsteady Aerodynamic Analysis of the Airfoil Profiles by Using Vortex Singularity Elements(Izmir Institute of Technology, 2018) Elmacı, Salim Cenk; Özbahçeci, Bergüzar; Özkol, Ünver; Özkol, Ünver; Özbahçeci, Bergüzar; 03.10. Department of Mechanical Engineering; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe steady and unsteady 2D flows around the airfoil were analyzed by utilizing the vortex singularity elements with two different inviscid flow models. Firstly, the steady flow was modeled in the light of steady state algorithm available in the literature. Then, the unsteady flow model was developed by some modifications on the algorithm of the steady flow. All the algorithms were transformed to the code in MATLAB® 2018a environment. For the steady state model, lift coefficients were compared with the inviscid and inviscid-viscous coupling models of the Xfoil 6.9 program data (Drela, 2001); and NASA experimental archive (Ira Herbert Abbott & Von Doenhoff, 1959). Since the model is inviscid, the reference point is the inviscid solvers; and the model agreed well with the Xfoil 6.9 inviscid mode for different type of airfoils. The unsteady model was created with three different operating modes; which are the sudden forward, heaving and the pitching. For the sudden forward motion, the lift and drag coefficients were compared with the studies in the literature. Besides, the lift, drag moment coefficients; and the wake patterns of the heaving and pitching motions were compared with the experimental data in the literature. The model is limited in terms of reflecting lift, drag and moment coefficients due to the not being included the viscous effects, flow separation, stall etc.; however, in terms of capturing the wake patterns, the model is quite useful.