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Farklı yüzer havuz tiplerinin sonlu elemanlar yöntemi ile yapısal analizi

Structural analysis of different types of floating docks by finite element method

  1. Tez No: 947970
  2. Yazar: BATUHAN ÇİFCİ
  3. Danışmanlar: DR. ÖĞR. ÜYESİ FUZULİ AĞRI AKÇAY
  4. Tez Türü: Yüksek Lisans
  5. Konular: Gemi Mühendisliği, Marine Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2025
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Lisansüstü Eğitim Enstitüsü
  11. Ana Bilim Dalı: Gemi İnşaatı ve Gemi Makineleri Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Gemi İnşaatı ve Gemi Makineleri Mühendisliği Bilim Dalı
  13. Sayfa Sayısı: 91

Özet

Yüzer havuzlar, su üstü araçlarının bakım ve onarım işlemlerinin karada daha hızlı ve maliyet etkin bir şekilde gerçekleştirilmesine olanak tanımaktadır. Farklı operasyonel gereksinimleri karşılamak üzere çeşitli konfigürasyonlarda tasarlanan yüzer havuzların dünya genelinde 30'dan fazla farklı tipi kullanılmakta olup her biri kendine özgü yapısal özelliklere sahiptir. Bu çalışmada, yaygın olarak kullanılan iki yüzer havuz tipi olan Rennie ve Keson (Caisson) tiplerinin geometrik tasarımı ve yapısal analizi sonlu elemanlar yöntemi ile gerçekleştirilmiştir. Keson tipi yüzer havuz, temel tasarım prensipleri Rennie tipi yüzer havuza dayanan, ancak mukavemet açısından daha gelişmiş bir yapıya sahip olan bir konfigürasyondur. Bu nedenle, çalışmada Rennie tipi yüzer havuzun modernizasyon yoluyla Keson tipine dönüştürülerek yapısal performansının nasıl iyileştirilebileceği de ele alınmıştır. Çalışmanın temel amacı, bu iki havuz tipinin yapısal farklılıklarının sehim (deflection) davranışı üzerindeki etkilerini incelemektir. Bu amaç doğrultusunda, öncelikle her iki yüzer havuzun üç boyutlu sonlu elemanlar modelleri oluşturulmuş ve analizleri gerçekleştirilmiştir. Analizlerde, gemilerin omurga blokları üzerindeki yük dağılımları, havuz yapısındaki gerilme ve deformasyon dağılımı gibi kritik yapısal faktörler ele alınmıştır. Model doğrulama aşamasında, gerçek bir havuzlama operasyonu sırasında alınan deneysel sehim verileri ile sayısal analiz sonuçları karşılaştırılmıştır. Havuzda yer alan analog ölçüm sisteminden alınan sehim verileri, model doğrulamasında referans alınarak hata oranı değerlendirilmiştir. Yapılan karşılaştırmalar sonucunda modelin, deneysel veriler ile uyumlu sonuçlar ürettiği tespit edilmiştir. Nümerik analizler sonucunda, Keson tipi yüzer havuzun Rennie tipine kıyasla daha yüksek yapısal mukavemete sahip olduğu belirlenmiştir. Rennie tipi yüzer havuzun braket bölgelerinde lokal gerilme yığılmaları tespit edilmiştir ve bu bölgelerde gerilme seviyelerinin malzeme akma gerilmesini aştığı görülmüştür (yalnızca lokal plastik şekil değiştirme). Buna karşılık, Keson tipi yüzer havuzda yapının genelinde oluşan gerilme değerleri akma gerilmesinin altında kalmaktadır. Ayrıca, yapılan sehim analizleri, Rennie tipi yüzer havuzun Keson tipi yüzer havuza kıyasla yaklaşık %38 daha fazla deformasyona uğradığını göstermiştir. Tüm bu bulgular, Rennie tipi bir yüzer havuzun modernize edilerek Keson tipine dönüştürülmesinin yapısal performansı artırmak için uygulanabilir bir strateji olduğunu ortaya koymaktadır. Sonuçlar, yüzer havuzların yapısal tasarım süreçlerinin optimize edilmesine ve mevcut yapıların modernizasyon yöntemleriyle güçlendirilmesine yönelik önemli mühendislik çıkarımları sunmaktadır.

Özet (Çeviri)

Floating docks enable the maintenance and repair of floating vessels to be conducted on land more efficiently and cost-effectively. Designed in various configurations to meet different operational requirements, there are more than 30 distinct types of floating docks in use worldwide, each possessing unique structural characteristics. This study focuses on the geometric design and structural analysis of two widely utilized floating dock types, the Rennie and Caisson, using the finite element method. The Rennie-type floating dock consists of independent pontoons and side walls, connected by structural elements, and represents a modular design widely used due to its production and maintenance advantages. The Caisson-type floating dock is a structurally enhanced configuration derived from the Rennie-type, maintaining its fundamental design principles while offering improved strength. A Rennie-type floating dock was modeled in this study using engineering drawings. The geometry (e.g., thickness) and material properties of an actual floating dock were incorporated into the finite element models. In particular, watertight bulkheads, frames, and other structural components of the shell model were established to replicate their real-world counterparts. During modeling, the choice of element types is guided by structural requirements and the desired level of accuracy. Four-node shell elements were used to model surface plates, bulkheads, decks, brackets, and other critical structural components of the floating dock's because they capture detailed stress distributions, including bending and membrane effects. Two-node linear beam elements were employed to represent frames and stiffeners. These structural components did not require the same level of localized stress detail as the aforementioned components, and the use of beam elements helped simplify the models and reduce computational costs while accurately capturing the global structural behavior. In summary, by strategically employing shell elements in high-stress and detail-critical areas and beam elements in less critical zones, the models achieved an optimal balance between accuracy and efficiency. A Caisson-type floating dock model was derived from the Rennie-type floating dock model. The spans between the pontoons were reinforced with bulkheads and frames, and the continuity of girders and longitudinal stiffeners, which served as the primary structural members, was maintained. To reduce the dock weight, the double-bulkhead configuration in the Rennie-type model was simplified to a single-bulkhead one in the Caisson-type model. Finite element analyses were performed using the Ansys software to characterize the structural behavior of the floating docks under actual loading and environmental conditions. The finite element model was validated through experimental measurements during an actual docking operation, and Numerical simulations were carried out under three ship loading cases: Ship model A, Ship model B, and Ship model C. Ship model C, which is currently docked in real life, was utilized for validation, and Ship models A (longer and heavier than ship model C) and B (similar in length but heavier than ship model C) were selected for analyses. These analyses enabled to evaluate the accuracy of the numerical model and elucidate critical parameters such as deflection and stress distribution for the floating dock types. Deflection data obtained from the actual docking operation were used to validate the finite element model. The maximum deflection in the simulation was determined to be ~76 mm at the center of the dock, consistent with the field-measured value of 75±5 mm. The relative error between the simulation and measured deflection values was within an acceptable range (≤9.0%), confirming the reliability of the finite element model. Simulation results revealed distinct differences between the two dock configurations under various ship loadings. Under ship model A loading, the Rennie-type floating dock model exhibited a maximum deflection of ~297 mm at the midsection and a maximum von Mises stress of ~592 MPa at the midsection brackets, exceeding the yield stress. Meanwhile, the global von Mises stress remained below 263 MPa. In contrast, under the same loading conditions, the Caisson-type floating dock model showed a maximum deflection of ~186 mm at the midsection and a maximum von Mises stress of ~259 MPa at the central bottom girder. Similarly, under ship model B loading, the Rennie-type model exhibited a maximum deflection of ~214 mm and a maximum von Mises stress of ~510 MPa at the midsection brackets. Meanwhile, under the same loading conditions, the Caisson-type dock displayed a maximum deflection of ~134 mm and a maximum von Mises stress of ~199 MPa. The von Mises stress in the Rennie-type floating dock model indicated that the stress levels in the midsection brackets exceeded the yield stress. Although this result did not affect the global behavior, further local investigation is suggested for a more comprehensive analysis as the level falls outside the elastic deformation range. Meanwhile, the Caisson-type floating dock model exhibited a maximum von Mises stress that remained below the yield stress in all regions, confirming that the whole structure remained within the elastic range (i.e., no permanent deformation was observed). the Caisson-type model exhibited ~38% less deflection than the Rennie-type model under all loading conditions. This suggests that converting a Rennie-type dock into a Caisson-type through modernization can enhance its performance, ultimately demonstrating that such modernization efforts significantly improve longitudinal strength, structural reliability, and operational efficiency. If the ballast tanks of the dock are filled to a level similar to that of under ship C loading case, the models were likely to experience around 40% less deflection when the ballast tanks were filled properly. The Introduction of ballast water into the end-section tanks reorganizes the dock's longitudinal load distribution and provides additional buoyancy force, effectively shifting mass away from the central region and mitigating stress and deflection along the midsection. All deflection values observed in this study remained below the limit suggested by relevant regulations (BV 1040, 1982). The maximum von Mises stresses were also lower than the yield stress (except only in small local regions). These two conditions indicate that the structure remained within the linear elastic zone; that is, the finite element models were consistent with the material properties and the deformed geometry. Although the finite element models were validated using experimental data, several limitations exist. The analyses were conducted under quasi-static loading conditions; that is, insignificant dynamic effects, such as wave loads and wind forces, were excluded. This study focused on a limited number of ship configurations and a single Rennie-type dock model. Moreover, conservative assumptions, such as the use of empty ballast tanks for ship models A and B, were made to simulate worst-case scenarios. Environmental factors and long-term fatigue performance were also beyond the scope of this study. Despite these limitations, the approach effectively delineated potential structural vulnerabilities and operational risks associated with aging dock designs. This research offers several key contributions that bolster academic research and practical engineering applications and fills a critical research gap in the performance comparison of floating docks under real operational conditions. Thus, it provides a practical solution for improving the safety and efficiency of docking operations. Additionally, the introduction of a deflection-based performance assessment methodology offers practical insights into optimizing docking operations and supports informed decision-making regarding modernization strategies. Further research involving additional ship configurations and dock models, various loading conditions, and long-term performance evaluations is recommended to demonstrate the full advantages of the proposed modernization approach.

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