Pham, Xuan Phuc
Green water and loading on high speed containerships.
PhD thesis, University of Glasgow.
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Green water problem and its loading effects on high speed containerships was investigated with the purpose of developing a modelling framework that can practically guide naval architects to a better understanding of this problem and improvements in design.
The research began by reviewing extensive publications relevant to the understanding of green water, limitations in the ways the problem had been addressed and establishing a methodology that could effectively unlock the physics and efficiently solve the problem.
As a first step, a summarised background to how green water started, developed and finally took place was presented. An experimental programme was then implemented in order to observe the occurrence and to explore the physics behind these events.
From the outcome of the experiments, it was obvious that green water modelling could be developed and solved by Computational Fluid Dynamics (CFD) technique through Volume of Fluid (VoF) method. To provide a starting point for this research, theoretical background of CFD was briefly introduced. Furthermore, in order to validate this approach, two benchmark tests were implemented and compared with published experimental data. It showed that in both cases, the simulation could accurately reproduce the results obtained from experiments.
Following this analysis, research continued to expand the CFD simulation to modelling of green water. Due to the complex and random nature of green water, development of the simulation framework was semi-empirical and based partly on experimental data. A pure theoretical approach could have been adopted. However, taking into consideration current limitations in ship motion prediction theories and sensitivity of green water to elemental factors, it was justified that semi-empirical approach was appropriate.
The simulation was conducted and the output results were compared with experimental results for a variety of test conditions that involved ship velocity, wave height and period. Good agreement between simulation and experiment was obtained. For all loading cases, experimental results were reproduced fairly well. This suggested that the modelling framework was adequate for all practical purposes.
Investigation was also conducted on a series of rectangular breakwaters that were fitted on the forecastle deck. Changes in water behaviour and loading following changes in the breakwater were well reflected. This implied that instead of a rectangular breakwater, the simulation model could also be applied to other types of breakwaters.
The results suggested that the simulation methodology has many practical applications. Within naval architecture, it can be used to perform parametric studies in order to select an optimal design of breakwater for a ship. In other sectors such as coastal engineering, the methodology can be adopted to investigate the interaction between water surge and a seawall or offshore breakwater.
In conclusion, it was found that the developed modelling framework shows potential for simple modelling of green water in which the behaviour of the water and its loading effects could be well reflected. It was further concluded that, provided appropriate principles are applied, the methodology has potential for other engineering applications. While it is acknowledged that current model may be limited by its semi-empirical basis and issues associated with computational requirements, it is noted that considerable possibilities for future research and development remains to be explored.
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