Ships Thruster Allocation Logic With Rudder Interaction

The minimum energy control of a ship´s motion with available thrusters is of interest. Precision control is needed for various ocean transfer and/or oil drilling support operations. Specialized ships are outfitted with fixed/ steerable thrusters in addition to the usual main screw(s) and rudder(s). The control of the available thrusters (thrust force and direction) to meet some desired surge, sway (forward, sideways) and moment command is sought. Often the number of thrusters to be controlled is greater than the number of commands (3). In this case, a unique minimum energy solution is selected from the infinite set of possible solutions. The present solution is a dynamic programming approach made efficient by special tactics for this class of problems. The methodology reported here is considered more general and provides a better solution in the sense of minimum energy and avoids the jump discontinuities encountered previously.