LEE- Gemi İnşaatı ve Gemi Makinaları Mühendisliği-Yüksek Lisans
Bu koleksiyon için kalıcı URI
Gözat
Son Başvurular
1 - 5 / 17
-
ÖgeHangar kenar modifikasyonu ile basitleştirilmiş fırkateyn modeli hava izinin iyileştirilmesi(Lisansüstü Eğitim Enstitüsü, 2025-01-23)Gemilerde konuşlandırılan operasyonel elemanlar için; geminin direnç, stabilite ve mukavemet gibi ana hesap unsurlarının yanı sıra harici hesaplara ihtiyaç duyulabilmektedir. Bunlardan biri olan helikopter güverteleri için, helikopterlerin güvenli iniş ve kalkış sınırlarını belirleyen uçuş zarfı hesaplarını yapmak önem arz etmektedir. Uçuş zarfı hesaplarının temelinde gemiye ait hava izinin modellenmesi yer almaktadır. Kaba yapılı süreksiz gövde tasarımlarına sahip gemiler, etraflarında türbülanslı yapıda hava akımı oluşturmaktadırlar. Helikopter güvertesinin kıçta olduğu bu tür gemilerde üst yapı aerodinamiğinin şekillendirdiği hava izi, helikopter operasyon bölgesinde daha karmaşık, asimetrik ve türbülanslı bir forma ulaşmakta, bahse konu türbülanslı ortam helikopter iniş kalkış manevralarında pilot kontrolünü zorlaştırmaktadır. Operasyonel verimliliğin artması, oluşabilecek kaza-kırımın önlenebilmesi ve pilot iş yükünün azaltılabilmesi amacıyla uçuş bölgesinde oluşan türbülansın doğru değerlendirilmesi önem arz etmektedir. Bu çalışmada bir basit fırkateyn şekli (SFS2) üzerinde oluşan akış rejiminin helikopter güvertesi bölgesine olan etkisi güncel Ölçek-Çözümlü Simülasyonlar (SRS) kullanılarak hesaplamalı akışkanlar dinamiği (HAD) ile incelenmiştir. Sonuçlar literatürde yer alan deney verileri ile kayda değer bir uyum göstermiştir. Kullanılan yöntemin hava izi hesaplamalarında öncelikli olarak kullanılabileceği değerlendirilmektedir. Askeri gemilerde üst yapı, aerodinamik kaygılar yerine düşük radar görünürlüğü öncelenerek tasarlanmaktadır. Gemilerin gizlilik kabiliyetini artırmak için eski üstyapı tasarımlarının yerini eğimli, düz yapılı, kaba tasarımlar almıştır. Bu yapılar gemi hava direncini artırırken helikopter güvertesi bulunan gemilerde uçuş bölgesindeki hava izini de karmaşıklaştırmaktadırlar. Gizlilik özelliklerinin yanında direnç ve hava izi iyileştirmelerinin sağlanabilmesi için ön dizayn aşamasında aerodinamik optimizasyon uygulanması önem arz etmektedir. Aerodinamik optimizasyon bütün üstyapıya uygulanabileceği gibi bölgesel olarak da uygulanabilir. Bu çalışmada gemi hava izi yapılanmasına odaklanıldığından, uçuş bölgesi civarında bir iyileştirme öngörülmüş ve Coanda etkisinden esinlenilerek hangar dış kenarlarına 5 farklı tipte yapı elemanı eklenmiştir. Uygulanan modifikasyonlar öncesinde sunulan aynı hesaplama yöntemi ile çözümlenerek sonuçlar yalın geometri ile karşılaştırılmıştır. Tüm modifikasyonlar hava izi türbülansını azaltmış, en iyi sonucu veren modifikasyon nihai karşılaştırmada sunulmuştur.
-
ÖgeComputational analysis of 2-d foils with and without ground effect in tandem(Graduate School, 2024-12-26)The flow behavior around tandem foils, both with and without ground effect, remains a complex and significant area of study, particularly as it plays a critical role in the design and development of wing-in-ground effect vehicles, sailing yachts, and hydrofoil vessels. Most existing numerical and experimental research on tandem configurations has been conducted at high Reynolds numbers exceeding 10⁶. In this comprehensive parametric study, the 2-D flow around two tandem NACA 4412 foils is simulated under both ground effect and free-flow conditions at a moderate Reynolds number of (Re = 3 × 10⁵). The angle of attack is fixed at 4° for both foils, and the effects of stagger distance (S), gap height (G), and ground clearance (H) are systematically investigated to assess their influence on the aero/hydrodynamic characteristics of the tandem system. The analysis begins by validating the aero/hydrodynamic performance of a single NACA 4412 foil without ground effect, followed by validation with ground effect. This step ensures the robustness of the computational framework before extending the analysis to tandem configurations. The incompressible RANS equations are solved using the finite-volume method, employing the SST k-ω turbulence model, which includes the γ-transport equation for enhanced turbulence modeling. This methodology enables a detailed examination of flow structures, pressure distributions, and the overall interaction between the foils in tandem arrangements under varying geometrical configurations. The results demonstrate that, consistent with findings from higher Reynolds number studies, tandem foils exhibit improved hydrodynamic efficiency compared to isolated foils, particularly when the gap height is positive, i.e., when the fore foil is positioned above the aft foil. Ground effect improves the aero/hydrodynamic performance of both isolated and tandem foils by enhancing lift and reducing drag. This phenomenon results in superior performance metrics compared to configurations operating outside of ground effect. In the tandem arrangement, the presence of the aft foil reduces drag on the fore foil due to increased static pressure between the foils, effectively exerting an upstream force on the fore foil. Conversely, the aft foil experiences an increase in drag due to the influence of the fore foil, a phenomenon observed across most tested configurations, with variations depending on stagger and gap distances. The interference effects between the tandem foils produce a range of outcomes; depending on the spacing, these effects can be either favorable or unfavorable in terms of drag reduction and overall aerodynamic performance. The effect of ground clearance on tandem foil configurations exhibits a similar trend to its influence on isolated foils in ground effect, characterized by an increase in both lift and drag coefficients as ground clearance decreases. These findings suggest that optimized tandem configurations can achieve significantly enhanced lift-to-drag ratios, particularly under positive gap heights, offering potential for performance improvements in wing-in-ground effect vehicles and other marine and aerospace applications. This research provides novel insights into the hydrodynamics of tandem foils operating at moderate Reynolds numbers in both ground-effect and out-of-ground-effect conditions. The outcomes of this investigation contribute to the ongoing development of next-generation wing-in-ground effect craft, hydrofoil systems, and other high-performance applications where tandem foil configurations can be utilized.
-
ÖgeShort circuit analysis in the marine L.V. A.C power systems:an essential aspect of shipbuilding industry(Graduate School, 2023)Short circuits in ship electrical systems can cause equipment failure, fires, and even death. As thus, short circuit analysis is an important component of ship design and maintenance. This thesis examines the importance of short circuit analysis in the shipbuilding industry, the problems it presents, and the strategies available for overcoming these hurdles. The thesis begins by discussing the various implications of short circuits, such as equipment damage, power outages, and safety risks. The basic principles of short circuit analysis are then explained, including fault current calculations, fault isolation, and protective equipment coordination. Following that, the thesis discusses the difficulties associated with short circuit analysis in the shipbuilding industry, such as the complex and large-scale nature of ship electrical systems, the difficulty of obtaining testing equipment, and the requirement for specialized tools and expertise. The study recommends a strategy to solve these issues, including the use of modern simulation tools for fault diagnosis, the establishment of standard operating procedures for testing and maintenance, and the training of ship employees in short circuit analysis and prevention. The importance of classification organizations, which create standards and give direction on short circuit analysis and prevention, is also discussed in the thesis. It underlines the need of collaboration with classification bodies in ensuring that ships satisfy safety and regulatory criteria. The paper ends by emphasizing the significance of short circuit analysis in the shipbuilding sector. It shows why this study is crucial for assuring the safety and dependability of shipboard electrical systems. In addition, the paper underlines the need of shipbuilders having a thorough grasp of short circuit analysis and its application in order to assure the safety and reliability of their boats. In closing, the study presents a thorough review of short circuit analysis in the shipbuilding industry, including its significance, process, advantages, and application. It is a valuable reference for shipbuilders and electrical engineers involved in ship design and construction. Shipbuilding processes typically take months, and sometimes even years, to complete. Therefore, it is crucial for the electrical design to progress in harmony with the ship's equipment, considering cost and tracking aspects. However, critical design milestones must be achieved for the project to commence. At this point, conducting accurate and timely short circuit calculations becomes vital. Even in cases where the necessary information for short circuit analysis is unavailable, the aim is to calculate the maximum short circuit current with minimal errors, thanks to industry standards published for the shipbuilding sector. Various strategies and measures will be researched and examined to minimize errors. In this way, project progress can continue without interruptions, and the electrical design can seamlessly integrate into the shipbuilding process. During this process, electrical system integrators take on significant responsibilities, ensuring the proper integration of electrical equipment on board and the smooth operation of all electrical products. They facilitate the correct integration of electrical equipment, as well as the balanced distribution of electrical loads. Finally, short circuit analysis is an important phase in the electrical design, safety, and dependability of a ship while it is being built. Although it presents difficulties in the shipbuilding industry, there are solutions available to overcome these difficulties and ensure that ships are designed, built, and maintained to the highest safety standards. In addition, the impact of power sources and electrical consumers on the maximum short circuit will be emphasized. Furthermore, the study explains how to perform calculations with insufficient consumer and generator information at the beginning of the project, and when and how these calculations should be updated through iterative methods. This study aims to contribute to the understanding of the factors necessary for accurate and reliable results in short circuit analysis. Within the scope of this study, 11 different types of vessels will be examined, including Fast Crew Suppliers, Motor Yachts, Tugboats, Cruise Vessels, Factory Longliners, Oil Spill Response Vessels, Freezer Trawlers, Trailing Suction Hopper Dredgers, Oil Tankers, Ro-Ro Vessels, and General Cargo Vessels. Various conclusions will be drawn using the data obtained from these vessel types. The objective of this study is to analyse the electrical loads and generator information of different vessel types and derive various insights based on this data.
-
ÖgeComputational investigation of the effects of the propeller diameter on the self-propulsion performance of a submarine at different forward speeds(Graduate School, 2023)The power generated by the propulsion system of a submarine must be used as efficient as possible due to a high propulsive efficiency reduces the dependency of the submarine to the surface and thus enhance its operational capabilities. Although several studies have been conducted in order to investigate the effects of the changes in a variety of parameters on the submarine self-propulsion performance up to now, some parameters are still needed to be discussed in more detail. The propeller diameter, one of the most important characteristics of the propeller geometry, is one of these parameters which needs deeper investigation into the topic. Since, the effects of the propeller diameter on the self-propulsion performance of the submarines are usually presented by some generalized diagrams in the open literature whose derivation methodology are not explained. The literature review in Chapter 1.1 which summarizes the past studies related to the field of the submarine hydrodynamics focusing especially on the submarine self-propulsion explains all other details and the developments regard to the topic over the years in the chronological order. On the other hand, further explanations for the base point of the study presented in this thesis exist in Chapter 1.2. In Chapter 2, the naval architectural based engineering terminology adopted throughout the study are described. In this context, definitions for the non-dimensional parameters which characterize the performance of the marine propellers and the propulsive factors of the submarines are given. In addition, the methods used for the open water and the self-propulsion analyses as well as the principles of the thrust identity and the torque identity methods are explained in Chapter 2. The present study utilizes the viscous flow based computational fluid dynamics methods for the analyses carried out with the aim of the investigation of the effects of the propeller diameter on the submarine self-propulsion performance. In this regard, RANS approach was used along with the SST k-ω turbulence model throughout the study in order to solve the incompressible flow around the bodies subjected to the examinations and the flow was assumed to be steady in the scope of the study. For the computations where the rotational motion due to the propeller is required to be modelled, the MRF method was additionally applied. The equations to be solved were discretized in the flow domain by means of finite volume method, on the other hand, the coupling between the pressure and the velocity terms was satisfied by the SIMPLE algorithm in order to solve these equations in an iterative manner. In Chapter 3, in-depth explanations are provided for these computational techniques among with their scientific basis starting from the introduce of the governing equations of the fluid dynamics. The application procedure of the GCI method which was used to assess the uncertainty due to the spatial discretization in the present study is also explained in Chapter 3. For the computational analyses, the fully-appended generic submarine model DARPA Suboff AFF8 was used whereas this submarine model was propelled by the generic INSEAN E1619 submarine propellers in different diameters. Three different INSEAN E1619 propellers having diameters of 0.262 m, 0.308 m and 0.354 m were selected which give reasonable values for the ratios of the propeller diameter to the maximum hull diameter to be 0.516, 0.606 and 0.697, respectively to propel DARPA Suboff AFF8. Further details about the geometries used are provided in Chapter 4. The computational process started with the verification and the validation studies which were required to proceed with the case studies. In this regard, the employed solution methods for the resistance characteristics of DARPA Suboff AFF8 and the open water characteristics of the full-scale INSEAN E1619 whose diameter is 0.485 m were verified and validated. Furthermore, a validation study for the self-propulsion characteristics of DARPA Suboff AFF8 propelled by INSEAN E1619 in 0.262 m diameter was also executed. The step-by-step explanations for the verification and the validation studies are presented in Chapter 5.1. After the solution strategies to be adopted were shown to be valid, the open water computations for the scaled INSEAN E1619 propellers were performed based on the structure of the verified and validated method employed for the full-scale INSEAN E1619. With these computations, the open water curves of these scaled propellers were obtained to be used in the stage of the calculation of the propulsive factors. In the next stage, the studies continued with the self-propulsion computations of DARPA Suboff AFF8 propelled by INSEAN E1619 propellers in the determined diameters to yield its propulsive characteristics at three different submarine forward speeds by using the validated method for its self-propulsion. Detailed information into the case studies are provided in Chapter 5.2. The data obtained by the computations were used as the input for the calculation of the propulsive factors of the propeller-submarine couples for three different forward speeds by utilizing from the thrust identity method. The variations of the obtained propulsive factors with respect to the ratio of the propeller diameter to the maximum hull diameter and the submarine forward speed were illustrated by the curves and an elaborate discussion was made through these relationships. Besides, the obtained data set by the present study were also compared with the previous data presented to the literature and discussed. The calculation of the propulsive factors and discussions on the obtained data are presented in Chapter 5.3 with all the details. On the other hand, the visual inspections which focus on to the features of the flow downstream the submarine were carried out by post-processing the data obtained from the self-propulsion analyses. Visualization studies are presented in Chapter 5.4 with their comprehensive discussions. It was demonstrated that the torque requirement of the propeller increases even though the propeller rotational rates at the self-propulsion points reduce as the propeller diameter increases. It was also detected that the propulsive factors are significantly affected by the propeller diameter being the Taylor wake fraction is the most affected one and its analysis requires a special attention in determining the propeller diameter of a submarine. Moreover, it was shown that the submarine forward speed affects all the propulsive factors except the propulsive efficiency. Also, it was observed that the trends of the curves drawn for the propulsive factors in the present study are in compliance with those of in the literature. Besides, it was visually demonstrated that the changes in the propeller diameter alter the wake flow of the submarine remarkably. Further concluding remarks in more detail along with the recommendations for the future studies related to the topic are provided in Chapter 6.
-
ÖgeYüzer güneş enerji sistemlerinde yapısal analiz(Lisansüstü Eğitim Enstitüsü, 2023)Artan enerji ihtiyacını karşılamak ve temiz bir enerji için güneş enerji panellerinin önemi günden güne artmaktadır. Özellikle son 15 yılda fotovoltaik panel fiyatlarının % 95 oranında ki düşüşü bu alanda ki yatırımları teşvik edici olmuştur. Fakat geniş alanlara ihtiyaç duyan güneş enerji panelleri aynı enerji miktarını üreten bir doğal gaz çevrim santraline nispeten 150 kat fazla alan işgal etmektedir. Özellikle geniş alanlara ihtiyaç duyan ülkeler ve arsa fiyatlarının yüksek olduğu yerler için maliyetin büyük bir kısmı alan maliyetine gitmektedir. Bu maliyetten kurtulmanın bir yolu olarak su üstü kurulumlar denenmiştir. Bu kurulumlarda güneş panellerinin sıcaklık sebebiyle daha verimli çalışabileceği bir ortam oluştuğu farkedilmiştir. Sistem kurulu olduğu rezevuarda ki buharlaşma sebebi ile doğal bir soğutma etkisi oluşturmakta bunun sayesinde de daha yüksek verimlilikte çalışabilmekte ve aynı zamanda su kütlesinin güneş ışınlarından büyük oranda korunması ile buharlaşma etkisini ciddi şekilde düşürmektedir. Verimlilik oranın soğutma etkisi ile panelde ki her bir derece için % 0,40 ile 0,65 toplamda % 10 – 25 arasında değişen miktarlarda arttırdığı gözlemlenmiştir. Doğa üzerine etkileri için yapılan araştırmalarda ise farklı görüşler olsa da çevreye fiziksel olarak faydalı kimyasal olarak zararlı olduğu fikri benimsenmiştir. YGES bileşenleri incelendiğinde temelde 5 bileşenin olduğu görülüyor. Bu bileşenler güneş enerjisi paneli, taşıyıcı dubalar, bağlama sistemi, kablolama ile sahil bağlantısı ve ankraj sistemidir. Yüzer sisteme etkiyen kuvvetler incelendiğinde; sistemin kendi ağırlığı, rüzgâr yükü ve hidrodinamik yükleri içermektedir. Tezde bu yüklerden ağırlık kısmı hesaplanmış diğerleri başka çalışmalardan alınmıştır. Tasarlanan duba konfigürasyonunda üç panel birbirine köşebentlerle bağlı ve 35°'lik ve 10°'lik ayarlanabilir açılarla dubalara rüzgâr yükü etkimektedir. Hesaplanan ve alınan yüklere göre dubalar üzerinde ANSYS programı ile sonlu elemanlar analizi yapılmış. Dubaların üzerinde ki düz yüzeyler farklı desenlerle değiştirilerek analizler tekrarlanmıştır. Seçilen desenler artı, çarpı ve yuvarlak şekildedirler. Yük ve yüzey alanı aynı olmasına rağmen oluşan gerilim değerleri farklı oluşmuştur. Düz yüzeyde 18,3 MPa, çapraz desende 16,9 MPa, artı desende 16,1 MPa ve yuvarlak desende 8,2 MPa değeri analiz edilmiştir. Elde edilen analiz sonuçlarına göre yuvarlak desenli dubanın çok daha mukavim bir yapıya sahip olduğu ortaya çıkmıştır. Yapılan bir diğer analizde ise Türkiye çevresindeki denizlerden elde edilen dalga yüksekliği ve sıklığı değerlerinden yola çıkarak yapılan yükleme koşullarında malzeme değişken gerilmelere maruz kalmıştır. Kulakçıklarda oluşan değişken gerilme yorulması hesapları sonucu güvenlik katsayısı olmamasına rağmen 3,09 yıllık ömür bulunmuştur. Fakat yüzer güneş enerji sistemlerinin her bir bileşeni için 20 – 25 yıllık ömür biçilmiştir ve hesaplanan ömür bunun çok altındadır. Bu sebeple açık denizlerde yüzer sistemlerin kullanımı yapısal anlamda kısa ömürlü olacağı sonucu elde edilmiş olur. Hidroelektrik santralinin kurulu olduğu barajlarda yüzer sistemleri kullanmak, invertör ve iletim hattı kablo maliyetlerini düşürecektir. Fakat hidroelektrik santralinin elektrik ürettiği süreçte ciddi su seviyesi değişimleri gözlemlenmektedir. Değişken su seviyesine ayak uydurabilen bir bağlama elemanı tipi henüz bulunmamıştır. Bu konuda tezde önerilen bağlama türü kazıklama tiptedir. Diğer kazıklama tiplerinden farklı olarak teleskopik boru sistemli bağlama ile yukarı aşağı yönlü hareket sağlanabilecek ve rulmanlar ile platform güneşin olduğu yöne kolayca döndürülerek enerji verimliliği arttırılacaktır.