Assessment of ship stability using dynamics

摘要

Currently, the intact stability of a ship is assessed using statical methods, which are based on concepts developed in the 1930s. To date, advances in the assessment of ship stability have been based on these statical concepts, and have not made any real attempt to take the full dynamics of a ship into account. Where the effects of waves are included this is based on empirical data which is only really applicable to a particular type of ship. What this means is that some ships are over penalized by requiring them to have stability levels far in excess of what is required by other vessels. This is of particular concern to new ship types. Recently, time domain non linear simulation models have been developed by a number of researchers in this field, which can be used to predict the extreme motions, including capsize, of a ship in severe sea states. The difficulty, however, is in determining a rational method to make use of these models to assess ship stability in a way which will result in a consistent level of safety against capsize for a range of vessel types. The main features of these simulation models, including validation, are presented, and the various approaches to using them to assess stability are discussed. A method based on running the simulation model in regular waves is proposed.