On the Hydrodynamics of a Monohull Ship in Following and Stern Quartering Seas
Doktorsavhandling, 2005

The demand for high-speed ships has been increasing by the years and high speed monohull ships are in common use for a wide variety of applications from fast general purpose workboats, pilot boats and patrol crafts to large naval vessels and fast ferries. It has been noted that a large number of high-speed monohull ships suffer relatively high risk for seakeeping problems in following seas, such as surf riding, broaching-to and reduced manoeuvrability in following and quartering seas. The present thesis contains results and discussions on hydrodynamics associated with ship motions in following and quartering seas. To study this subject, first experimental methods have been used but also theoretical and semi-empirical methods have been applied to the current problem. Comparisons of results from experiments and calculations were also carried out, discrepancies in these results are discussed in the present thesis and the conclusions can, among others be used to evaluate possibilities for computations on the present problems. Traditionally seakeeping of ships is studied by using a linear strip theory, which implies a high degree of simplification regarding the fluid mechanics for a ship navigating in waves. A fine presentation of the strip theory is given by Salvesen et. al in reference [17]. However this theory's degree of simplification means that seakeeping analysis of a ship navigating in following, or stern quartering seas is most often not within the scope of the strip theory. In order to develop tools for analysis of the current matters a study on hydrodynamic forces on a semi-planing monohull in following and stern quartering seas has been performed. The present thesis is based on the work described by the listing below: Development of a method for testing and evaluation of a ship in full-scale or a free running ship model. A scale model was tested in various regular waves as well as a few irregular waves consisting of two and three components. The model was fixed in the surge, sway, roll and yaw directions but free to heave and pitch. This setup gave possibility to measure the most important forces and still having a realistic displacement, or wetted surface, for the ship model. This test methodology gives opportunity to use a relatively limited number of model trials for identifying conditions where surf riding and broaching-to are likely to occur. The purpose with the trials is also to validate numerical computations of hydrodynamic forces. Numerical computations using a code based on a modified strip theory and semiempirical methods. A comparison of computations and the experimental work. Reference: [17] Salvesen et al., 'Ship Motions and Sea Loads' SNAME Transactions, vol. 78, 1970.


Olov Lundbäck

Chalmers, Sjöfart och marin teknik, Fartygs drift och säkerhet





Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 2311

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