Seakeeping Predictions Of A Container Ship By Using Actual Wave Database

It is a significant task of researchers and designer to evaluate a ship, especially a new ship design, which possesses excellent seakeeping or not. But nowadays at the preliminary design state, most studies of performance of a ship are based on the calm water resistance of the ship hull without considering the sea condition prevailing on the route that the ship is designed to operate. A great lot of facts indicate that the ship which has fine speed in the calm water perhaps don't have good seakeeping performance in real sea state. We all know that ships must be navigated in the ocean finally, therefore the investigating of ship's seakeeping should combine the actual ocean environment. For a long time, the method of ship navigating in seaway mostly relies on tie experience of masters and weather routing service and developing a set of empirical navigational methods, however without the guidance of theory, sometimes there would appear some fatal mistakes and bring on some catastrophic results. From this aspect, it needs us urgently to investigate the ship's seakeeping combining the actual ocean environment. The seakeeping is not the result that single factor affects, but is the result that many factors affect together, so we must look for a scientific synthetic method to evaluate the seakeeping of ships based on the effects of all factors. Only by this way we could obtain a correct conclusion that would give the ship designer and masters an effective guidance. This paper embarks the research of the comprehensive evaluation method of seakeeping and its application, basing on the fruit of the academic prediction of seakeeping. Fist, according to the 2nd law of Newton this dissertation discusses the motion performance of ship navigating in waves and sets up a series of linear equations of ships response in regular waves in case of linearity based on the strip theory. Solving the equations obtains the six degrees of free amplitude response function of ship motions in seaway. Utilize the theory of linear system of stationary stochastic processes and its recommendation on depicting wave spectra of ITTC, obtain various seakeeping factors' motion response spectral density function in stochastic waves of ship, then utilizing the knowledge of statistics obtain the changing curves of various seakeeping factors' significant amplitude with the changing course and speed, from above we can discover the connection between navigational mode and various ship's motion performance. Then apply the wave data of ocean environment, according to the related theories, to calculate and analyze the long-term prediction of ship's seakeeping, moreover obtains some significant conclusions. Finally, the research introduces a computational method of comprehensive evaluation index (the percentage of the task time of ships) which can reflect the entire performance of seakeeping of ships, then apply the method to calculate and analyze the percentage of the task time of ships based on the wave data of ocean environment, and also obtains some significant conclusions.