An engineering prediction method for large amplitude motions of ships in waves is presented in the paper, based on the commonly used strip theory with the extension of taking into account the instantaneous variation of the wetted hull surface during motions and its effects on the ship hydrodynamic characteristics. The method is examined on the large amplitude hull motions, the relative bow motions to waves and the instantaneous forces on the hull etc. for a ship of Series 60 in waves. It is hoped that the present method can be widely used in the concept ship design stage due to its. simplicity and efficiency.
The investigation of large amplitude motions of ships in waves and the corresponding prediction technique is drawn much attention recently due to its significance in many research aspects such as the performance of deck wetness, bow slamming, hull loading, relative motions with the wave elevation etc. Although some more or less rigorous theoretical methods, 3-D time domain method for example, exist for this purpose, application is still limited due to the great computational costs. In practice, to seek an engineering approach for the estimation of large amplitude motions of ships in waves, which is rational in theory while practical in engineering, is regarded of significance, especially for the use at the initial ship design stage. In the linear frequency domain, one of the practical approach is the well known strip theory first presented by Korvin-Kroukovsky (1955). Since then, some improvements have been achieved. Among them, we may list the new strip theory (Tasai and Takagi, 1969), rational strip theory (Ogilvie, 1969), STF method (Salvesen, Tuck, and Faltinsen, 1970). Kim's strip theory (Kim, Chou and Tein. 1980) etc. The computational results of those methods coincide well with the experimental ones, especially for the longitudinal motions.
