Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Structural Health Monitoring of Small-Scale Vertical Axis Wind Turbine Blade(Izmir Institute of Technology, 2023) Öğünç, Ozan; Turan, Gürsoy; Turan, Gürsoy; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologySon yıllarda, Dünya genelinde ve Türkiye'de enerji fiyatlarında büyük artışlar yaşanmaktadır. Bu artışların yanı sıra fosil yakıtların doğaya verdiği zarar yenilenebilir enerji kaynaklarına olan ilgiyi daha da arttırmıştır. Yenilenebilir enerji kaynaklarından olan rüzgar, bu ilginin odak noktalarından biri olmuştur. Rüzgardan gelen kinetik enerjiyi elektrik enerjisine dönüştüren rüzgar türbin sistemleri farklı mühendislik hizmetlerinin uygulanması ile oluşturulur. Dünyadaki hızlı teknolojik değişim ve rüzgara olan ilgiden dolayı son yıllarda rüzgar türbin sistemleri çok hızlı bir şekilde gelişme göstermiştir. Rüzgar türbinlerinin sayısının ve öneminin artması ile bu tarz yapıların sağlığının incelenmesi önemli bir konu olmuştur. Bu tez çalışmasında, XGEN-Energy firmasının ürettiği Wind-Er modelinin kanadı incelenmiştir. Türbin kanadının öz frekanslarını ve mod şekillerini belirlemek için python dili kullanılarak, kovaryans güdümlü stokastik alt uzay tanımlama yöntemi (SSI-Cov) programlanmıştır. Çalışma iki temel kısımdan oluşmaktadır. İlk kısımda, kanat modeli python yazılım dili ile parametrik tasarım yapılmış ve CalculiX sonlu elemanlar programı kullanılarak modal analizi yapılmıştır. Modal analiz tamamlandıktan sonra uygun deney düzeneğine karar vermek için transient analizi yapılmıştır. Analiz sonucu çıktı verileriyle SSI-Cov yöntemi test edilmiştir. İkinci kısımda, kanadın fiziksel modeli üzerinde testler yapılmıştır. Sayısal model ile fiziksel model çıktı verileri birbirini doğrulamıştır. Modelin modal parametrelerinden, doğal frekansları ve ilk modun mod şekilleri SSI-Cov kullanılarak tahmin edilmiş ve sonuçlar tutarlı çıkmıştır.Master Thesis Investigation of Tsunami Induced Hazards in the Floating Docks of Seferihisar Sığacık Marina by Numerical Modeling(Izmir Institute of Technology, 2023) Çeli̇k Karaca, Hi̇lal; Özbahçeci̇, Bergüzar; 01. Izmir Institute of TechnologyTsunamiler neden oldukları su seviyesi değişimleri ve güçlü akıntılar nedeniyle liman içindeki yapılarda önemli hasarlar meydana getirebilirler. 30 Ekim 2020 tarihinde Sisam (Samos) Adası kuzeyinde meydana gelen 6.6 Mw büyüklüğündeki deprem, deniz tabanındaki düşey deformasyona bağlı olarak tsunamiye yol açmıştır. Tsunami Seferihisar'daki Teos Marina yüzer iskele pontonlarında ağır hasarlara neden olmuştur. Literatürde tsunaminin denizde ilerlemesi, kıyıda tırmanması ve baskın mesafeleri ile ilgili çok sayıda çalışma olmasına rağmen tsunami kaynaklı su seviyesi değişimlerinin ve akıntının, zincirlerle tabandaki tonozlara ve birbirlerine bağlı yüzer iskele pontonlarında oluşturduğu hasarın henüz incelenmediği görülmüştür. Tsunaminin yapılar üzerindeki hasar seviyesinin tespit edilmesi ve azaltılması için sayısal modelleme oldukça önem taşımaktadır. Bu çalışmada, Teos Marinada yer alan ve en çok hasar gören yüzer iskele olan A iskelesi orta doğruluklu hidrodinamik model, ANSYS™ AQWA® kullanılarak sayısal olarak modellenmiştir. Çalışmada öncelikle tsunami etkileri olmaksızın yüzer iskelenin stabilitesine bakılmıştır. Daha sonra tsunamiden dolayı oluşan su seviyesi değişimleri ve akıntı etkileri modelde yapıya etki ettirilmiştir. Yapının deplasman ve rotasyonları incelenmiş, zincirlerin gerilmeleri, ve pontonlar arasındaki bağlantılar üzerindeki kuvvetler hesaplanmıştır. Tonozlar için kayma ve yukarı kalkma güvenlik katsayılarına bakılmış ve stabilite durumları kontrol edilmiştir. Tüm bu sonuçlar tsunami sırasında ve sonrasında Marina yetkililerinin ve görgü tanıklarının gözlemleri, çekilen fotoğraflar ve yapılan ölçümlerle karşılaştırılmıştır. Buna göre, tsunami sırasında gözlendiği gibi, pontonların yükselip alçalması, zincirlerin kopması, ponton bağlantılarının kopması, tonozların yukarı çıkması modelde de simüle edilebilmiştir.Master Thesis Numerical Modelling of Failure in 3d Quasi-Brittle Unreinforced Structural Components(Izmir Institute of Technology, 2022) Özdemir, İzzet; Özdemir, İzzet; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyConcrete 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) Özdemir, İzzet; Özdemir, İzzet; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThere 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 Effect of Fines and Ground Acceleration on Liquefaction Resistance of Silty Sand: Numerical Study(Izmir Institute of Technology, 2022) Tozburun, Batuhan; Ecemiş Zeren, Nurhan; 01. Izmir Institute of TechnologyLiquefaction is a phenomenon that damages structures that have not been adequately studied during the design process. While improving the performance of the buildings under dynamic loading conditions, it is essential to evaluate the liquefaction behavior of soils under the dynamic load. In this thesis, the constitutive soil model (UBCSand Model), which can simulate liquefaction, is used within the finite difference methods (FDM). First, results are compared with the laboratory test results to verify numerical liquefaction simulations. The physical and mechanical tests performed at Izmir Institute of Technology (IZTECH) are used as an input for the soil model. Then, a series of constant volume cyclic direct simple shear results (CDSS) tests performed for the same silty sands were used to verify the numerical study (Tutuncu, 2021 and Monkul, 2021). CDSS tests were performed on mixtures of clean sands and three non-plastic silts at different contents of 0%, 5%, 15%, and 35% allowing for observing the liquefaction response of silty sands of different grades (Monkul, 2021). The laboratory tests performed at Yeditepe University and Izmir Institute of Technology were combined to study the effect of fines content and relative density on cyclic liquefaction resistance of silty sands. The aim of this thesis is to perform a numerical model to evaluate the effect of fines content (FC), ground acceleration (amax) and relative density (Dr) on liquefaction resistance. The FDM model gives similar results to laboratory test results. Hence, the model can be used to assess the liquefaction with different soil models and conditions.Master Thesis Developing Flood Mitigation Measures for Baledwayne City, Somalia, by Using the Hec-Ras Model(Izmir Institute of Technology, 2022) Tayfur, Gökmen; Tayfur, Gökmen; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThis study covers the investigation of the flood mitigation measures required to protect the city of Baledwayne, which is located in the Hiran region of Somalia and has been subject to frequent floods recently. In the HEC-HMS model, the precipitation data measured in 2019 and DEM at the Baledwayne and Bulo-Burti stations of the Hiran region were used as input. The observed discharge in the Shabelle river in 2019 of both stations was imported into the model to compare the simulated rainfall-runoff hydrographs. The rainfall-runoff hydrographs of 2019 were simulated with the HEC-HMS model using these parameters, SCS Curve Number for analyzing runoff volume, Snyder Unit Hydrograph for estimating direct runoffs, and Constant Monthly for calculating the baseflow and Muskingum for channel routing. The outflow hydrographs at both stations were successfully simulated. With the 1D&2D HEC-RAS model, flood maps were generated using various alternatives to protect the study area from floods of Q500 flow rate with a return interval of 500 years. The Deyr 2019 flood event was used for the calibration of the model. The model determined the flood extent and depth of this flood event by changing the roughness coefficient at specific intervals. Various flood mitigation measures have been investigated after calibration. It has been found that the best protection can be achieved by the combination of these four flood mitigation measures: (1) rehabilitation of the Warabole diversion channel, (2) construction of detention ponds at the upstream of the floodplain, (3) levees along both sides of the river and (4) improvement of the river.Master Thesis Performance of Sand Granulated Rubber Mixture for Soil Stabilization Using Discrete Element Method (dem)(Izmir Institute of Technology, 2022) Kadekeshova, Kuralay; Ecemiş Zeren, Nurhan; 01. Izmir Institute of TechnologyThe results of a detailed analysis of the capability of numerical approach Discrete Element Method (DEM) to replicate a physical model of a sheet pile foundation in dry soil under static loads are presented in this study. Accordingly, the DEM software Particle Flow Code 2-Dimensional (ITASCA, 2019) is used to model experimental tests. Numerical model of direct shear test on clean sand and sand mixed with 10% granulated rubber has been done to calibrate the micromechanical parameters of the granular materials, such as sand and rubber particles. The particle sizes, density, interparticle friction coefficient, and contact stiffness of the discrete elements were determined and used in DEM simulations of sheet pile foundation. A total of four DEM models of the sheet pile foundation with different sand-rubber mixture backfill area were tested and analyzed in PFC2D. The loading process speed, contact stiffnesses, and porosity of the system had a significant impact on the deformation parameters of the sheet pile and lateral pressure distribution of the sand-rubber mix backfill. In this study two measurement methods were investigated. First, the measuring particles of the sheet pile particles were used, whereas the second, the measuring circles were placed behind the sheet pile foundation. The measurement circles proposed by (ITASCA, 2019) were suitable for the DEM model. Numerical outcomes showed a relative good match with the physical model. Finally, the ability of the PFC2D code as a discrete element approach in modelling of cohesionless granular material and sheet pile foundation is confirmed in this work.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 Trend and Drought Analysis of Three Stations in the Puntland State of Somalia(Izmir Institute of Technology, 2022) Muse, Nur Mohamed; Tayfur, Gökmen; Tayfur, Gökmen; 03.03. Department of Civil Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyLong-term rainfall and temperature records were used to analyze drought features as well as temperature and precipitation trends in Somalia's north area from 1980 to 2020. Monthly records are being used at three locations (Bossaso (station 1), Qardho (station 2), and Garowe (station 3).Deciles, Discrepancy precipitation index, percent normal, Gamma, log normal, and normal-SPI were used to examine the Drought. The past extreme and severe droughts that occurred in the early 1980s and throughout the course of the last two decades are being detected using the log-SPI, gamma-SPI, PN, and Deciles The Mann Kendall (MK) test, Spearman's rho (SR test), and the Şen trend test were used in the trend analysis to identify trends in time series, and the Pettitt test to detect change points in time series. In contrast, the Thiel-sen Approach was used to estimate the magnitude of the slope in the precipitation and temperature time series. The average temperature and annual precipitation are increasing by about 0.3C per decade and 3 mm per year, according to the trend analysis results.Master Thesis Influence of Soil on Cone Penetration Resistance-Shear Wave Velocity Correlation(Izmir Institute of Technology, 2022) Örücü, Murat; Ecemiş Zeren, Nurhan; 01. Izmir Institute of TechnologyMany researchers proposed correlations between cone penetration resistance (qc) and shear wave velocity (Vs). The researchers used the datasets they obtained by performing laboratory or field tests while developing their correlations. The qc measurements were made with CPT test and Vs measurements were made with in-situ tests (SCPT, DHT, CHT). The proposed correlations were very different from each other. The existing correlations between qc and Vs are given in two ways: The soil type-dependent correlations and different correlations for different soil types. The soil type-dependent correlations were limited and also there is no change depending on fines content . Therefore, it would be useful to determine a correlation based on soil type with soils with different fines content. In this study, CPT and SCPT tests were performed in the getechnical laboratory of IZTECH to investigate the influence of soil type on qc-Vs correlation. Tests were performed on clean sand and sand - non-plastic silt mixtures having 5%, 15%, and 35% fines content at different relative densities inside the soil box. CPT profiles and Vs values were obtained to develop a relationship between Vs, and qc based on soil type index (Ic). The Ic values were found using CPT-based approaches found in the literature. A new soil type-dependent correlation to predict the Vs of soils from qc is presented in this study. The new equation was compared with existing correlations. The equation is useful to estimate Vs from CPT measurements for all soil types with different fines content.