A comparative evaluation of the behaviour of some typical floating offshore structures

It is commonly accepted that, during the design process, the characteristics of the location play a major influence leading to the design wave principle. In fact, as compared to ship design process, in case of offshore structures including the ship shaped ones, conceptual design plays a decisive role regarding the capability to safely operate at zero speed on locations in order to reach a high operational index in rough seas. This is directly linked to the limits of the accelerations due to body behaviour in waves which are clearly stated related to the comfort on board corresponding to different types of activities (intellectual work, manual work etc.). On the other hand, the above mentioned restrictions and the operational limits related to the body motions amplitudes, need to be considered. Consequently, the body geometry as well as the masses distribution solutions is mandatory to be carefully evaluated taking also into account the direct influences on the induced structural loads. To this purpose, a comparative evaluation of the Response Amplitude Operators (RAO’s) has been performed for six different bodies consisting in an AHTS ship, a floating crane, a semisubmersible and a group of three pipe laying vessels. The results presented in the paper could be useful when future development of activities on a certain location is envisaged providing quantitative data as well as qualitative ones, giving reliable information depending on the geometry and mass distribution.