Dynamics and control of ocean systems

Industrial activities at sea have increased in the last 50 years; this has been due mainly to the exploitation of oil and gas. Many technological problems have been overcome, however new challenges appear every day. New oil fields have been discovered in reservoirs with different geological profiles, sea depth, distance from shore and varying environmental conditions. In addition, international regulations have become more stringent in order to reduce the potential for accidents and to minimize their consequences. Among the many challenges, the study of how to control the position of a floating vessel and its dynamics has caught the attention of researchers around the world as most of the offshore industry vessels need to work while remaining stationary. The dynamic positioning system has been a worldwide solution for keeping a vessel stationary especially in cases of short-term operations. This chapter deals with the modelling of the dynamics for a ship-like vessel under the forces of current, wave and wind, assuming low speed, and presents some wave frequency filters and control laws for the dynamic positioning system.