This paper reports comparative experiments with two novel and one conventional thrust control algorithms for the unsteady (transient) control of thrust generated by conventional bladed-propeller marine thrusters. Hybrid simulations combining actual real-time experimental thruster responses with simulated one dimensional real· time vehicle dynamics show the model-based thrust control algorithm to offer vehicle position control superior to that of its non-model-based counterpart.
A growing body of theoretical and experimental literature indicates that an essential element of improved underwater vehicle positioning systems is improved unsteady (transient) dynamical models of the bladed thrusters commonly used to actuate dynamically-positioned marine vehicles [13, 1,7,8, 3]. Our companion paper [12] describes three different candidate models for unsteady thruster dynamics and compares actual experimental thruster responses to model predictions. This recent work by various researchers toward more precise thruster dynamics models will find application in three principal areas. First, incorporating precise models of thruster dynamics into the closed· loop feedback systems of marine vehicles promises to enable more accurate real· time control of thrust force and, in consequences improved vehicle positioning speed and accuracy. Second, the incorporation of accurate thruster dynamics models in computer simulations of underwater vehicle motion might improve the precision with which these simulations can predict actual vehicle motion. Third, insight obtained by a detailed understanding of unsteady flow and dynamics of marine thrusters might enable improved thruster mechanical design. This paper reports work towards the first goal stated above - improved vehicle closed-loop positioning. The paper is organized as follows: Section 2 proposes three novel thrust control algorithms derived from, respectively, the three thruster dynamical models reported in [12]. Section 3 examines the effect of the three different thrust control algorithms on closed-loop vehicle positioning accuracy. The section reports hybrid simulations combining real-time experimental thruster responses with simulated one dimensional real-time vehicle dynamics.