Deplasman Tipi Gemiler için Sayısal Analizlerin Gerçeklemesi ve Doğrulaması

Year 2021, Issue: 219, 77 - 95, 30.06.2021

Sarih Sarı , Ali Doğrul

Abstract

Gemilerde güç ihtiyacı ve yakıt tüketimini en aza indirmek çok önemlidir, bu sayede daha çevreci gemiler elde edilmiş olur. Bu hedef, gemilerin hidrodinamik performansının tahmin edilmesi ile elde edilebilir. Bu bağlamda, çeşitli araştırmacılar tarafından deneysel ve sayısal yöntemler yaygın olarak kullanılmaktadır. Deneysel çalışmalar model deneylerine dayanırken sayısal yöntemler viskoz ve potansiyel akış kabullerine dayanmaktadır. Bu çalışmada çeşitli tipte gemiler sayısal olarak incelenerek hem gerçekleme hem de doğrulama adına kapsamlı bir veri setinin sunulması amaçlanmıştır. Sayısal yöntemin doğruluğunu ve hassasiyetini göstermek adına iki konteyner gemisi ve bir muharip suüstü gemisi için RANS denklemlerini çözen sayısal bir yaklaşım kullanılmıştır. Bu gemiler KRISO konteyner gemisi (KCS), Duisburg test gemisi (DTC) ve ONR (Office of Naval Research) tarafından geliştirilen teknedir. Bu gemiler etrafındaki akış incelenirken serbest yüzey etkileri hesaba katılmıştır. Akış analizleri sakin su koşullarında gerçekleştirilmiştir ve gemiler paralel batma ve trim hareketine karşı serbest bırakılmıştır. Belirsizlik çalışması için ITTC ve AIAA tarafından önerilen GCI yöntemi kullanılmıştır. Sık, orta ve seyrek olacak şekilde ağ boyutu ve zaman adımı açısından farklı analiz setleri kurgulanmıştır. Bu analiz setleri sabit bir iyileştirme oranıyla \left(\sqrt\mathbf{2}\right) oluşturulmuştur. Belirsizlik amaçlı sayısal analizler her bir geminin dizayn Froude sayısında gerçekleştirilmiştir. Belirsizlik değerleri toplam direnç açısından elde edilmiştir. Bunu takiben, düşük ve orta hızları kapsayacak şekilde geniş bir Froude sayısı aralığında her bir model gemi için kapsamlı bir doğrulama çalışması yapılmıştır. Doğrulama, sayısal sonuçların erişilebilen deneysel sonuçlarla kıyaslanmasıyla yapılmıştır. Buna ek olarak, sonuçlar literatürde mevcut diğer sayısal sonuçlarla karşılaştırılmıştır. Doğrulama, toplam direnç, paralel batma ve trim açısı parametreleri üzerinden yapılmıştır. Bu çalışma, hesaplamalı akışkanlar dinamiği (HAD) yönteminin gemi hidrodinamik performansını yeterli düzeyde tahmin edebildiğini göstermiştir. Bu sonuçlara göre karşılaştırma için deneysel veri eksikliğinde sayısal yöntem düşük belirsizlik değerleriyle güvenilirdir.

Keywords

Karşılaştırma, HAD, RANS, Toplam Direnç, Toplam Direnç, Belirsizlik, Doğrulama

Verification and Validation of Numerical Simulations of Displacement Type Vessels

Abstract

It is crucial to reduce the power need and fuel consumption of ships, thus eco-friendly ship design can be achieved. This goal can be achieved with the accurate prediction of the hydrodynamic performance of ships. In this manner, numerical and experimental methods are widely used by many researchers. Experimental studies are based on towing tank tests while the numerical methods are based on viscous and potential flow assumptions. In this study, it is aimed to investigate different types of ship models to provide a comprehensive data set. A numerical approach solving RANS (Reynolds-averaged Navier-Stokes) equations was employed for two container ships and a naval surface combatant to show the precision and accuracy of the numerical method. These vessels are KRISO container ship (KCS), Duisburg test case (DTC) and ONR Tumblehome (ONRT) developed by the Office of Naval Research. The flow around these vessels was investigated by taking the free surface into account. The flow analyses were carried out in calm water conditions and the ships were set to be free to sinkage and trim. For the verification study, the GCI method, which is recommended by ITTC (International Towing Tank Conference) and AIAA (American Institute of Aeronautics and Astronautics), was employed. Fine, medium and coarse cases were generated with different grid sizes and time step sizes. These cases were generated by using a constant refinement ratio\ \left(\sqrt2\right). The numerical analyses for the verification purpose were conducted at the design Froude number of each model ship. The uncertainty values were obtained for the total resistance. Following this, a comprehensive validation study was conducted for each ship model in a wide range of Froude numbers, covering low and moderate speeds. The validation was done by comparing the numerical results with the available experimental data. In addition to this, the results were compared with other existing numerical results in the literature. The validation was done in terms of total resistance, sinkage and trim parameters. This study showed that the computational fluid dynamics (CFD) method can sufficiently estimate the ship’s hydrodynamic performance. Within these results, when there is a lack of experimental data for comparison, the numerical method is again reliable having low spatial and temporal uncertainty values.

Keywords

Benchmark, CFD, RANS, Total Resistance, Uncertainty, Validation

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