An optimal control system for pitch, heave and roll stabilisation of surface vessels

A six degree of freedom mathematical model is used to compute the motion of a large vessel travelling in head and beam seas. The model is constructed from a set of nonlinear time-varying differential equations and contains fourteen state variables, six control variables and six disturbance variables. Pitch, heave and roll are controlled by two forward and two rear stabilisation fins, each independently controlled. An optimal control law is developed so that the motion is minimised according to some predefined cost function. An optimal solution is sought that provides a global minimum for the important state variables concerned. The extent of the reduced ship motions are analysed and conclusions drawn as to the effectiveness of such a system and whether its implementation can be justified. >