Optimal thrust allocation for marine vessels

This paper presents a new thrust-allocation scheme which significantly reduces the fuel consumption for dynamic positioning of ships when rotatable azimuth thrusters are used. Thrust allocation is the problem of determining the thrust and the direction of each of the n thruster devices of a ship, given the desired forces and moment from the control law. The problem of singular configurations is pointed out and solved by using a modification of the singular-value decomposition. A filtering scheme is proposed to control the azimuth directions to reduce the wear and tear, and to minimize the required thrust and power in a general manner, allowing the enabling and disabling of thrusters. Both new theory and full-scale sea trials are presented. Copyright (C) 1997 Elsevier Science Ltd.