Discrete Near-Optimal Wave Disturbances Rejection Control for Offshore Platforms With Delays in Measurement and Actuator

The wave disturbances rejection control problem for linear discrete jacket-type offshore platforms with delays in measurement and actuator is studied. Taken the delays in measurement and actuator into account, the linear model of the jacket-type offshore platform is established in discrete domain, in which the external wave forces are generated from a designed exosystem based on the JONSWAP wave spectrum and linearized wave theory. A delay-free model from the model of the jacket-type offshore platform with delays in measurement and actuator is formulated based on a designed discrete transformation vector, and the system output with delays in measurement is reformed into a corresponding delay-free form. Then, the discrete near-optimal wave disturbances rejection controller (NOWDRC) is derived from the reformed delay-free system and the corresponding system output in respect of an average quadratic performance index, which is made up of a system state feedback item, a wave disturbances feedforward item and a controller memory item. Finally, simulation results demonstrate that the system output under proposed NOWDRC, including the displacement and velocity of the jacket-type offshore platform, can be offset to smaller values than those under a classic feedback optimal vibration controller, and the delays in measurement and actuator can be compensated effectively.