Delayed non-fragile H∞ control for offshore steel jacket platforms

© The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.This paper is concerned with a delayed non-fragile H∞ control scheme for an offshore steel jacket platform subject to self-excited nonlinear hydrodynamic force and external disturbance. By intentionally introducing a time-delay into the control channel, a delayed robust non-fragile H∞ controller is designed to reduce the vibration amplitudes of the offshore platform. The positive effects of the time delays on the non-fragile H∞ control for the offshore platform are investigated. It is shown through simulation results that (i) the proposed delayed non-fragile H∞ controller is effective to attenuate the vibration of the offshore platform; (ii) the control force required by the delayed non-fragile H∞ controller is smaller than that required by the delay-free non-fragile H∞ controller; (iii) the time delays can be used to improve the control performance of the offshore platform.