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ABSTRACT
In the present work, a seakeeping analysis of a containership of 139,96m length, is performed. The study includes the linear seakeeping analysis, coupled heave and pitch motions, uncoupled roll motion, in irregular waves, heading angle 0 ÷ 360 deg., with Pierson-Moskowitz wave power density spectrum. The numerical seakeeping analyses are carried on with an original DYN OSC program code based on linear seakeeping method and statistical short term prediction response method. Taking into account the specific limits of seakeeping criteria, the dynamic response statistical polar diagrams are obtained for each motion degree and the cumulative one, pointing out the influence of the ship speed and heading angle for seakeeping assessment.
Keywords: numerical seakeeping analysis, dynamic response, seakeeping criteria
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1. INTRODUCTION
An analysis of seakeeping characteristics of a ship moving in regular waves and irregular waves actually involves the analysis of ship behaviour in waves [1].
The evaluation of seakeeping performance of a ship largely depends on the environmental conditions and defined criteria and this is the main reason that any comparison related to the ship speeds, the influence of heading angles, loading conditions, etc.. is a complex problem.
Seakeeping analysis is essentially a three part problem [2] :
1. estimation of the likely environmental conditions to be encountered by the vessel,
2. prediction of the response characteristics of the vessel,
3. specification of the criteria used to assess the vessel's seakeeping behaviour. This also defines the way in which the performance of different vessels is compared.
Evaluation of seakeeping performance of a ship shall be based on its oscillations in different states of the sea that is expected to encounter during its lifetime. The procedure starts with the predicting hydrodynamic characteristics of the ship response for several speeds and heading angles. In irregular waves, short-term and long term distributions can be used to estimate the most probable maximum values of responses.
Magnitude increase movement in varying degrees of severity can then be predicted, using wave spectra representative for the selected operational sea areas. Usually, the sea state is described by a theoretical wave spectrum [3]. Finally, the capacity of the ship can be estimated on the basis of probability of the remaining ship movements within acceptable limits.
In...