Wave feedforward control for dynamic positioning vessel under swell-dominated floatover condition: A numerical and experimental study

Abstract

Dynamic positioning (DP) floatover has become a widely adopted method for installing the topsides of offshore structures due to its cost-effectiveness and precise positioning capabilities. In swell-dominated seas, the thrusters of a DP vessel generate periodic forces that can lead to wear and tear on the actuators and potentially result in thruster failure during floatover operations. The usage of thrusters is a limiting factor in such conditions. This paper introduced a novel method to mitigate reciprocating forces using wave height prediction and feedforward control during floatover operations. A Kalman observer was employed to reconstruct the wave field in real-time based on wave height measurements obtained from the four legs of the jacket, which enabled the estimation of wave height at the center of the vessel and the prediction of swell frequency motion. By employing gain scheduling, the resistance from DP thrust was minimized. Numerical simulations and model-scale experiments demonstrated the effectiveness and adaptability of the proposed feedforward algorithm compared to two basic motion observers. The proposed methods significantly reduced the periodic thrust on the DP vessel, thereby overcoming the limitations of floatover operations in swell-dominated sea states.