Dynamic positioning operability assessment by using thrust allocation optimization

A Dynamic Positioning system can automatically maintain both the position and heading of a vessel by using its thrusters. The core is composed of force and thrust allocation modules that tailor the required forces and moment to compensate the external forces over the available actuators. The propulsion systems are often over-actuated and, then, it is impossible to solve analytically the thrust allocation algorithm. To address the challenge several methodologies are available, starting from reducing the order of the problem up to operation research techniques. The paper aims to develop an optimisation procedure that includes an ad-hoc objective function with relative non-linear constraints for the thrust allocation logic that tends to minimize the thrust of the actuator. The procedure accounts for non-linear hydrodynamic effects on the thrust generation, including thruster-thruster and thruster-hull interactions. Based on the assumption of equal available power, two different propulsion configurations are investigated in terms of yearly operability.