Tersanelerdeki İş Kazalarının İstatistikî Olarak İncelenmesi

Increase of shipyard accidents at Tuzla shipyards in Turkey has attracted public attention towards shipbuilding sector and the activities at shipyards have undergone a close scrutiny. In this paper, shipyard accidents both here in Turkey and in the world were studied statistically. Within the context of this study, accidents occurred in Hong Kong, Singapore, USA and the UK has been analyzed and evaluated in terms of their causes and effects in a wider perspective. Some conclusions have also been drawn based on the data availabl

CFD simulations of vertical ship motions in shallow water

The seakeeping behaviour of a vessel in shallow water differs significantly from its behaviour in deep water. In shallow water, a vessel’s motion responses to incident waves will be affected by hydrodynamic effects caused by the presence of a finite depth. Given that a vessel will sail in shallow water at various times during its service life, such as when entering harbours, it is important to have an understanding of the influence of shallow water on ship motions. In this study, using a commercial unsteady Reynolds-Averaged Navier-Stokes solver, a numerical study of ship motions in shallow water was carried out. Firstly, the characteristics of shallow water waves were investigated by conducting a series of simulations. Then, a full-scale large tanker model was used as a case study to predict its heave and pitch responses to head waves at various water depths, covering a range of wave frequencies at zero speed. The motion results obtained were validated against related experimental studies available in the literature, and were also compared to those from 3-D potential theory. The results were found to be in good agreement with the experimental data. Finally, it was shown that vertical motions were significantly affected by shallow water

Comparative seakeeping performance analysis of a warship

A successfully designed ship is expected to fulfill her mission in almost all weather and sea states without compromising her safety. This is particularly important for a warship and crew onboard to be able to perform their complex tasks in good physical and mental state. This paper presents comparative seakeeping performance analysis of a warship operating in Turkish waters, which include Mediterranean Sea, Aegean Sea and Black Sea, for varying sea states, wave headings and ship speeds. The comparative analysis was conducted by using a commercial seakeeping package (ShipmoPC), which is a strip theory based software, for the 6 degrees of freedom motion responses as well as the vertical accelerations, and added wave resistance. The effect of active fins on the roll motion responses was also explored. The analysis results were compared with the NATO Standardization Agreement (STANAG 4154) criteria. The results were presented in standard graphical format and polar diagrams, and discussed in details in the paper

Influence of mixed flows on ship hydrodynamics in dredged channels

Although there is a significant body of research devoted to the shallow water hydrodynamic aspects of ships, several unexamined topics remain. Among these is that of critical outer flow in a dredged channel and its influence on parameters of interest. While empirical methods can be used with ease to resolve this, they can provide results with reliability sufficient only for an early design stage. On the other hand, more sophisticated potential flow theories are either inapplicable or do not perform well at the critical limit. However, RANS (Reynolds Averaged Navier-Stokes) – based tools can accurately capture all underlying phenomena without relying on limiting assumptions. This paper presents an attempt at comparing some results obtained via a CFD-based RANS solver and the slender body theory for critical outer flow in a dredged channel

Numerical study on wave run-up height and depression depth around a vertical circular cylinder at various froude numbers

The turbulent flow past a circular cylinder has been studied extensively by previous researchers due to its importance in many engineering applications. In particular, the wave run-up is one of the most significant design factors when offshore structures are operated. In this paper, the wave run-up height and depression depth around a vertical circular cylinder were numerically investigated. The commercial CFD solver “STAR-CCM+” has been used for the numerical simulations. The models of K-epsilon turbulence and volume of fluid (VOF) are utilised to solve the Reynolds Averaged Navier-Stokes equations (RANS) and continuity equations, respectively. Various Froude numbers and Reynolds numbers are utilised to observe the wave run-up height on the front of the cylinder and the depth of depression at the back. The results were compared with previous experimental data and theoretical values and were found to be in good agreement with other studies

A numerical investigation of the squat and resistance of ships advancing through a canal using CFD

As a ship approaches shallow water, a number of changes arise owing to the hydrodynamic interaction between the bottom of the ship’s hull and the seafloor. The flow velocity between the bottom of the hull and the seafloor increases, which leads to an increase in sinkage, trim and resistance. As the ship travels forward, squat of the ship may occur, stemming from this increase in sinkage and trim. Knowledge of a ship’s squat is necessary when navigating vessels through shallow water regions, such as rivers, channels and harbours. Accurate prediction of a ship’s squat is therefore essential, to minimize the risk of grounding for ships. Similarly, predicting a ship’s resistance in shallow water is equally important, to be able to calculate its power requirements. The key objective of this study was to perform fully nonlinear unsteady RANS simulations to predict the squat and resistance of a model-scale Duisburg Test Case container ship advancing in a canal. The analyses were carried out in different ship drafts at various speeds, utilizing a commercial CFD software package. The squat results obtained by CFD were then compared with available experimental data

Full-scale unsteady RANS simulations of vertical ship motions in shallow water

The seakeeping behaviour of a vessel in shallow water differs significantly from its behaviour in deep water. In shallow water, a vessel’s motion responses to incident waves will be affected by hydrodynamic effects caused by the presence of a finite depth. Given that a vessel will sail in shallow water at various times during its service life, such as when entering harbours, it is important to have an understanding of the influence of shallow water on ship motions. In this study, using a commercial unsteady Reynolds-Averaged Navier-Stokes solver, a numerical study of ship motions in shallow water was carried out. Firstly, the characteristics of shallow water waves were investigated by conducting a series of simulations. Then, a full-scale large tanker model was used as a case study to predict its heave and pitch responses to head waves at various water depths, covering a range of wave frequencies at zero speed. The motion results obtained were validated against related experimental studies available in the literature, and were also compared to those from 3-D potential theory. The results were found to be in good agreement with the experimental data. Finally, it was shown that vertical motions were significantly affected by shallow water

A validation of a pivoted point absorber type wave energy converter using CFD

Wave energy is sustainable and clean energy, so it has great potential to be an eco-friendly and lasting renewable energy resource in the future. Recently, a number of researchers have investigated different types of wave energy converters (WECs) using numerical models such as potential theory and Computational Fluid Dynamics (CFD) to enhance the efficiency of such devices. In this paper, a validation of a point absorber type WECs is investigated to capture the movement of the WEC system and to measure the moment on the WEC system. The WEC consists of a lever and a buoy. The geometry is the same as the existing experimental geometry of the reference in order to validate the present numerical simulation. The buoy is connected to the lever and has a hinge on the connection point. Besides, another hinge is installed in the middle of the lever, and the WEC system rotates in the pitch direction. The commercial CFD package Star-CCM+, which solves Reynolds-Averaged Navier-Stokes equations, is employed in this study. In the initial stages of this research, a validation study against published experimental results was conducted. The rotational displacement and the moment on the buoy were compared with the existing experimental data of the reference. The result shows good agreement. In the near future, a study on a new pivoted point absorber WEC device regarding the buoy shape of the WEC device and an operation principle will be performed based on this numerical study

Numerical modelling of the nearfield longitudinal wake profiles of a high-speed prismatic planing hull

This study investigates the level of accuracy with which Computational Fluid Dynamics (CFD) is capable of modelling the nearfield longitudinal wake profiles of a high-speed planing hull. It also looks to establish how various set-ups influence the accuracy, with a specific emphasis on turbulence modelling. It analyses a hull over a broad range of conditions to provide detailed insight into the strengths and limitations of CFD, comparing the numerical results to the experimental results previously generated by the authors. A quantitative comparison is made for the centreline (CL) and quarterbeam (QB) longitudinal wake profile plots. Following this, a qualitative comparison is made between photos of the flow pattern from the experimental testing and free surface elevation plots from CFD. The study concluded that CFD is an accurate and robust method of modelling the nearfield longitudinal wake profiles of a high-speed planning hull

Strategies to minimise numerical ventilation in CFD simulations of high-speed planing hulls

Numerical Ventilation is a well-known problem that occurs when the Volume of Fluid method is used to model vessels with a bow that creates a small, acute entrance angle with the freesurface, typical for planing hulls and yachts. There is a general lack of discussion focusing upon Numerical Ventilation available within the public domain, which is attributable to the fact that it only affects such a niche area. The information available s difficult to find, often fleetingly mentioned in papers with a different focus. Numerical Ventilation may be considered one of the main sources of error in numerical simulations of planing hulls and as such warrants an in-depth analysis. This paper sets out to bring together the available work, as well as performing its own investigation into the problem to develop a better understanding of Numerical Ventilation and present alternate solutions. Additionally, the success and impact of different approaches is presented in an attempt to help other researchers avoid and correct for Numerical Ventilation. Interface smearing caused by the simulations inability to track the freesurface is identified as the main source of Numerical Ventilation. This originates from the interface between the volume mesh and the prism layer mesh. This study looks into the interface to identify strategies that minimise Numerical Ventilation, presenting a novel solution to prism layer meshing that was found to have a positive impact. Through the implementation of a modified High Resolution Interface Capture (HRIC) scheme and the correct mesh refinements, it is possible to minimise the impact of Numerical Ventilation to a level that will not affect the results of a simulation and is acceptable for engineering application