LEE- Gemi ve Deniz Teknolojisi Mühendisliği-Doktora
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ÖgeManeuvering of high speed displacement vessels in regular waves(Graduate School, 2023-10-16) Sarıgül Öztürk, Deniz ; Kınacı, Ömer Kemal ; 508192103 ; Shipbuilding and Ocean EngineeringThis doctoral thesis presents a comprehensive exploration of maneuvering performance in waves, aiming to gain insight into the interactive behavior of waves and vessels and use this interaction to develop a mathematical model of maneuvering in waves. The research focuses on the adaptation of experimental methods, practical system-based methods, and computational analysis techniques to enhance the integration of solution methods. The central objective of this thesis is to systematically reveal the complicated characteristics of mean wave drift loads. Additionally, the thesis aims to demonstrate the influence of these loads on the assessment of maneuvering performance. The research seeks to bridge the gap between traditional investigation of maneuvering in calm water and growing demand for determining the minimum propulsion power needed to maintain a ship's maneuverability in adverse conditions. The study employs a systematic approach, combining various research techniques. It utilizes a system-based mathematical method along with laboratory experiments and simulation-based analyses to achieve its objectives. The methodology encompasses theoretical modeling, computational simulations, and practical measurements. The research reveals that integrating mean wave drift loads, namely surge wave drift force, sway wave drift force, and yaw wave drift moment, obtained with a practical experimental approach or computational methods, can significantly enhance the capacity of system-based models. The data reduction procedure enables to reach of zeroth-frequency values representing the mean wave drift loads. This thesis contributes a novel approach to research endeavors, experimental initiatives, and software development projects aimed at elucidating the concept of "maintaining maneuverability" in challenging sea conditions. The findings underscore the importance of adapting wave conditions to maneuvering applications developed with new approaches. The insights from this research hold wide-ranging implications for ocean engineering practitioners and researchers. The presented framework offers a holistic perspective that can guide maneuvering performance and navigational safety. The findings of this thesis will be also presented in the activity named "Assessment of Experiments and Prediction Methods for Naval Ships Maneuvering in Waves", the activity period of which is 2021-2023 and still continues. The activity is carried out within the scope of Applied Vehicle Technology (AVT) and is referred to by the code AVT-348. In conclusion, this doctoral thesis presents a practical experimental and numerical approach to achieve surge, sway, and yaw wave drift loads in regular waves which are then used to demonstrate the effect of wave-related loads on the maneuvering performance of surface vessels. The measured wave drift forces and moments are incorporated into the equations of motion for maneuvering to predict the effect of waves on the maneuvering performance of a vessel. A simplified mathematical model to show the behavior of the vessel in waves is represented by four nonlinear equations of motion for surge, sway, yaw, and roll. The turning circle, which is one of the standard maneuvering tests is simulated for ONR Tumblehome (ONRT) at different wave conditions in order to demonstrate the effect of wave drift forces on the trajectories and time histories of maneuvering parameters.
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ÖgePhysical investigation of 2d free falling wedge(Graduate School, 2023-06-23) Yasa, Ahmet Mertcan ; Kükner, Abdi ; 508132101 ; Shipbuilding and Ocean EngineeringWater entry is an important phenomenon for sea-going vessel in terms of planing and slamming. Pressure distribution on the solid surface, at the moment of impact on water is a critical parameter during the initial design and optimization of a vessel, especially on planing vessels, trawlers or free-fall lifeboats and alike. The aim of this study is to create a simple yet accurate method to aid ship designers on the initial process & optimization of the ship design. Porpoising motion of planing hulls or releasing the free-fall lifeboat from the ship during the emergency situation are perfect two examples of this specific design problem. During this specific water impact event, none of the vessels shall suffer any kind of damage which results in either structural failure on the said vessel or injuries/death of persons onboard. It is fair to say that this specific design factor has its importance to this date. Starting from this point of view, for the easiness of the calculations a wedge shape is taken into account for both planing vessels and trawlers & fishing vessels. This wedge shape can be considered as similar to planing hulls, small craft such as trawlers or free-fall lifeboats. Based on Wagner's famous method for calculating pressure distribution and pile-up of water on plates, this study proposes a new method using Schwarz-Christoffel conformal mapping to calculate pressure distribution along the surface as well as pile-up of water and force history. At the beginning, the definition between mapping plane and real plane is presented. By doing this, pile-up coefficients are calculated. Based on the Wagner's flat plate theory, the pile-up coefficients are plotted from 0 degrees of deadrise to 90 degrees deadrise, where 0 degrees deadrise is a flat plate. The results are further compares against Mei's results [17], which are not only improving the Wagner's fixed pile-up coefficient but also found by similar conformal mapping method. Upon calculating the pile-up coefficient, this coefficient incorporated into existing empirical methods for individual usage. Then, conformal mapping calculations are continued to plot pressure distribution along the wedge. The pressure distribution values are compared against Yettou's Experiment [15], Oien's Experiment [54], Sun's Results [36] and Dong's Experiment [20]. These experiments consist of respectively 25 degrees of deadrise, 30 degrees of deadrise, 10 degrees of deadrise and 45 degrees of deadrise. The results are very well matching. Upon completion of comparison, the force history is calculated. The force history is compared against Sun's results, which are consisting of four different impact speeds. It is found some overestimation on the force history, but in general results are satisfactory. As an additional verification, comparison against real ship sections was also examined. This proposed method can be expressed on monotonic sections. Based on this method of application, alternative sections were proposed against real ship sections and comparison for slamming pressure is conducted. Results were discussed accordingly. Lastly, a comparison against CFD application is done. The results are shown as very well matching. By doing this, presented method in this study was compared against drop test experiments, real ship sections and CFD application all together. It is accuracy proved in all aspects. In conclusion, the aim is considered to be achieved by presenting pressure distribution and force history results by making different comparisons. This study provides an easy method to calculate this critical design factor. It is noted that the method is very accurate for initial impact loads and can be used in initial design stage to understand the loads and pressure along the ship section.