Effects of small time-delays on dynamic output feedback control of offshore steel jacket structures subject to wave-induced forces

This paper is to investigate the effect of a small time-delay on dynamic output feedback control of an offshore steel jacket structure subject to a nonlinear wave-induced self excited hydrodynamic force. Firstly, a conventional dynamic output feedback controller is designed to reduce the internal oscillations of the offshore structure. It is found that the obtained controller is of a large gain in the sense of Euclidean norm, which demands a large control force. Secondly, a small time-delay is introduced intentionally to design a new dynamic output feedback controller such that (i) the controller is of a small gain in the sense of Euclidean norm; and (ii) the internal oscillations of the offshore structure can be dramatically reduced. It is shown through simulation results that purposefully introducing time-delays can be used to improve control performance.