Active vibration H∞ control of offshore steel jacket platforms using delayed feedback

This paper is concerned with delayed H ∞ control for an offshore steel jacket platforms subject to external wave force. By artificially introducing a proper time-delay into control channel, a delayed H ∞ controller is designed to attenuate the wave-induced vibration of the offshore platform and thereby improve the control performance of the system. The problem of the controller design is transformed into a nonlinear minimization problem. It is shown through simulation results that compared with the delay-free H ∞ control scheme, the vibration amplitudes of the offshore steel jacket platform with the delayed H ∞ control scheme are in the same level as the ones with the delay-free H ∞ control scheme, while the required control force by the delayed H ∞ control scheme is much smaller than that by the delay-free H ∞ control scheme. Compared with the feedforward and feedback optimal control scheme, both the vibration amplitudes of the offshore platform and the required control force with the delayed H ∞ control scheme are smaller than the ones with the feedforward and feedback optimal control scheme.